Most WoW raiders are literal brainlets. They rely on DBM to do literally everything for them which speaks to how badly fights are designed there where it needs an addon not even developed by the WoW devs themselves for people to do anything correctly. You should see some of their raids and all the nonsense that appears on their screens along with annoying automated call outs like hearing "BEWARE" every 2 fucking seconds. And seeing big text of "LOL X MECHANIC IS ABOUT TO BE DONE, MOVE 2 INCHES TO THE RIGHT" or "X SPELL IS BEING CASTED BY THE BOSS, DODGE IT LOL"
So having a bunch of people that are so used to having their hands held coming to a game that expects you to actually study the fights and react accordingly instead of waiting for a computerized voice to tell you what to do is going to take time for them to adjust to the mechanics of the game. Playing WoW for so long has rotted their ability to think critically on their own because they are so used to be told what to do by a raid leader. These extreme fights can literally be pugged and no one can say a single word to each other and still be able to complete the fight to perfection. It's a case of they are both making it more complicated and harder than it actually is or needs to be and they need literal giant neon signs telling them where to go and what to do because if not, they just stand around like a bunch of retards and take mechanics to the face.
It doesn't help that having boosted, they have no idea what each individual mechanic marker is, they don't know what a stack marker is, they've never done a previous fight that required them to break a tether so when they see a tether they sit there with their thumbs in their asses and wondering why they keep taking tics of damage, they don't look at and read a buff while in a water puddle to know that it gives them resistance to fire damage so common sense would tell you to stand in one of those when the big giant FIRE FIST appears and targets someone to hammer, they don't know that the big glowing circle around them means they're gonna get hit with an aoe attack and anything else caught in that circle is going to get hit as well, they've never done anything at all in the game previously that teaches them these things.
I guess if they are gaining a certain level of enjoyment out of trying to figure out a fight that isn't even that hard, then it's okay. It can be frustrating for veterans to watch them flail about like idiots when they could have taken their time to learn so that it wouldn't be as difficult for them as they make it for themselves. Hopefully if they aren't even more retarded, they'll retain what they learned so when they see similar markings in the future, they'll instinctively know what to do.