Cody, the Young Bucks, they get it. I really think the Hot Topic deal made them all realize that the business is capable of being changed into a millennial pop culture thing.
Really the success of AEW is sorta a series of events that fell into place. This is going to be a long post, so if you're not a sperg for wrestling like me you can skip it:
In 2010, Colt Cabana reaches out to a t-shirt maker on behalf of his then-friend, CM Punk. Punk needs a custom-made shirt that says "I BROKE BIG SHOW'S HAND", and wants to commission it himself. Today, that t-shirt maker is ProWrestlingTees.com. Combined with Colt's move into podcasting, Cabana also uses the t-shirt maker to make his own merch much more easily than before, and starts to make a very good living for himself as an independent wrestler with various other interests, thus demonstrating that it is, indeed, possible to hustle and make a living outside the WWE or, at that time, TNA.
If we really want to trace things back, I think we should start at Punk's pipebomb promo. Technically we can go way back to, as mentioned before, Omega leaving Deep South Wrestling and taking a chance on working Japan full time, but that didn't necessarily get the ball rolling on all this happening, it just put Kenny in the right place to be there when stuff did start taking shape and he could actively participate in furthering it. That promo, particularly "Maybe I'll defend the belt in New Japan Pro Wrestling...maybe I'll go back to Ring of Honor...", was the moment even the most casual WWE fan now had the prospect of looking at the wider wrestling world so clearly placed on TV, as it appeared the potential for Punk showing up in either place could be integrated into a WWE main event storyline. It didn't lead to that, obviously, but you have to think it got a lot of attention on those places.
It also just so happened that around that time was when NJPW was getting its renaissance on track, with Tanahashi and Nakamura firmly established as their top stars (the year began with Tanahashi dethroning Kojima for the IWGP title at Wrestle Kingdom V) and the Kidani-led project to get Okada and Naito in the main event just about to get underway, particularly Okada's return the next year. That said, yes, it has to be pointed out that at this time Okada was in TNA getting absolutely nothing to do while on excursion, but it was during this time and while in TNA that he made contact with people like the Bucks. ROH, meanwhile, gets bought by Sinclair near this time, in June of 2011, and while Sinclair has clearly never had designs on pumping in enough money to get ROH to the next level, it at least stabilized the company and turned it into a more secure place to get full time work for some wrestlers. Things remain pretty stable for the next couple of years, until early 2013: NJPW books an angle where Prince Devitt betrays Ryusuke Taguchi, teams up with Bad Luck Fale, and starts making little finger gun gestures at the camera and toward his opponents, leading to not only a hugely successful foreign heel stable being formed, but having Bullet Club serve as a sort of gateway for western fans to start noticing NJPW more, while also offering more full-time roster spots to foreign talent. Early in the stable's run, Okada, just over a year since his return from excursion in TNA, recommends that NJPW bring the Bucks in to join the gaijin stable as their junior heavyweight tag team.
2013 is also around the time that the storyline begins that eventually gets Cody into his Stardust gimmick, an idea he runs with at first, but eventually leads to diminishing creative returns. Attempts to get to work more with his brother, to integrate his father, and to get his ideas heard and taken seriously in WWE aren't really working the way he wants them to, and frustration is building for him. Around this time, Ring of Honor and New Japan begin a working relationship that sees talent exchanges, Young Lion excursions, and each promotion's belts defended on the other's bigger cards at times. The Bullet Club brand begins to spread with more North American exposure via this relationship. It is notable that TNA has slipped considerably during this time, and ROH, while bigger than ever, is limited in their growth, again, due to Sinclair not looking to invest too heavily in it. A bit later, AJ Styles can't come to an agreement with TNA on a new contract and leaves for NJPW, suddenly bringing a whole lot of new eyes to the product as he joins Bullet Club the same night that Devitt has his final match before leaving for NXT. AJ main events, wins the IWGP title, and soon Wrestle Kingdom 9 is getting aired on American PPV through Global Force Wrestling (no, seriously, that's who allowed it to happen), which just so happens to feature an IWGP Jr. title match involving a newly-signed and heel-turned Kenny Omega, who's immediately spending a whole lot of time around the Young Bucks, the trio quickly christening themselves the "Elite" squad within Bullet Club.
2015: Samoa Joe leaves TNA, like AJ Styles before him, and returns to Ring of Honor unannounced. Shortly afterward, Joe arrives in NXT unannounced. While WWE quickly used a clause in Joe's contract to lock him into an exclusive deal, the message is clear - if you're a big enough name and want to bank on yourself, the wrestling terrain is shifting to the point where you can negotiate the kind of contract that wouldn't have been imagined possible just a couple of years earlier. Next domino to fall: AJ wants to get back to spending more time working in the United States, and is looking to either sign with WWE or return to TNA on a better deal now that he's upped his name value again. He approaches Matt Jackson about coming with him as a package deal, but Matt tells him that while he's grateful, he and Nick had just signed new contracts with ROH and NJPW. AJ instead departs at just about the same time and negotiates new deals alongside Bullet Club members Gallows and Anderson, instead, to get them all into WWE. This opens the door to Omega getting booked to forcibly remove Styles from Bullet Club and assume leadership over the group, and NJPW is quick to throw their booking behind him, putting him over Hiroshi Tanahashi for the Intercontinental title in his first marquee match as a heavyweight and having him become the first gaijin to ever win the G1 tournament when it's held that summer.
Seeing the writing on the wall, the final piece gets moved into place: Cody Rhodes is pushed to his limit with WWE, and wants out. He leaves, and he makes no bones about wanting to experience all the growing international and indie scene has to offer, even becoming the first wrestler to perform at WWE's Wrestlemania, TNA's Bound for Glory, ROH's Final Battle, and NJPW's Wrestle Kingdom in less than one year. He joins Bullet Club during this time and finds kindred spirits with the Elite; while often booked as adversaries on-air, the group grows close, with Cody even becoming a regular on the burgeoning "Being the Elite" YouTube channel, which starts to shift from a travelogue and documentary of life as a multi-continent wrestler to a regular vehicle for storylines, comedy, and character development.
The same night that Cody debuts in NJPW, Kenny Omega also has his first ever match against Kazuchika Okada. The "Six Star Classic" creates waves around the wrestling world, and the paradigm of what people are expecting from their wrestling is shifted. Meanwhile, Chris Jericho, content to just work WWE now and then to mostly promote new tours for Fozzy, has the idea for a "Jericho Cruise", featuring bands and pro wrestling from around the world, including NXT. WWE refuses, Jericho gets annoyed, and soon he's reaching out to New Japan through Don Callis about facing Kenny Omega at Wrestle Kingdom 12. At the same time the Elite group just gets bigger and bigger, and soon, alongside Marty Scurll and Adam Page, they're getting merchandise deals at Hot Topic for themselves and New Japan, they're getting Pop Vinyl figures, and they're getting offers from all over, including from WWE. The Bucks make public that they're interested in getting to spend less time traveling across the ocean, but the group decides they're going to do all they can to stick together, eventually getting the idea that between them they had enough talent and contacts within the industry to put together something bigger. Cody cooks up the idea for All In, and Dave Meltzer's famous tweet about ROH or any non-WWE company not being able to fill a 10,000 seat venue in 2018 gives Cody the chance to take that idea public. The show, done through ROH but also including talent from all over the growing indy scene, is a hit, and becomes a proof of concept for a new promotion.
Finally, in late 2018 and early 2019 we get the Bucks not getting the exact contract offers they're seeking from ROH and NJPW, Tony Khan getting involved, and that's that.
So AEW is in large part about Bullet Club's evolution, the limits Sinclair placed on ROH, the fall of TNA, a missed connection where AJ might've gotten the Bucks into WWE, Cody and Jericho getting sick of WWE's stifling creative environment, and then getting the right combination of personalities all getting friendly with one another, along with them connected with a long time pro wrestling fan with very deep pockets, with a ton of that stemming from CM Punk kind of giving fans a chance to see non-WWE wrestling as cool and counterculture following the pipebomb promo.