Vince mostly* got rid of managers because his mentality was "Why the absolute fuck should I invest time and money into a wrestler who can't fucking talk?" and for the most part he was correct. Back in the early 90s when the WWE was teetering on the edge managers made a load of sense because it allowed them to make the most out of what he had, but in the modern era where the WWE is loaded and can hire whoever they want, whenever they want it makes no sense to pay for a manager to elevate some guy when there's 20 guys graduating from the Performance Centre EVERY YEAR who could just about do their job.
*What's funny is that Vince DIDN'T get rid of managers, he still dished them out for generational talents like Brock Lesnar. He just didn't give them out to every 'potential' guy that popped up so it allowed them to either develop their promo skills or fuck off.
Managers don't make sense anymore in the wrestling world that WWE created.
A manager was suppose to be a business manager. In kayfabe, they were a guy that would handle your affairs, help you move up the card and make you more money. Any yokel in the crowd can understand that dynamic. More than being a mouthpiece, a manager was an easy way to cosign new talent for the crowd. A modern example would be when Bobby Heenan hugged James E. Cornette when Cornette debuted in WWF. You didn't need a video package to explain him to audience. Bobby Heenan is an asshole, he's friendly with this faggot, that faggot must be an asshole too. BOOOOO
Paul Heyman isn't a manager. He's an advocate. He's a person you can put on tv when Roman or Brock don't want to show up. He can't elevate talent. Nobody in the audience believes that having Paul Heyman in the corner gives that wrestler an edge. He's a character in a play.
Same with referees. They use to just be guys that would enforce the rules during a match. It made sense to say their names. To give them credibility. When Earl Hebner called a match, you knew it was going to be straight.
Now the audience has been told a million times that the referee is a human walkie-talkie who's job it is to give time cues and directions from the truck. Who gives a fuck what sheboon nigger's name is?
It's the same reason why injury angles no longer work. Everybody knows that it's an angle and, who cares if it isn't, they have guaranteed money. Your favorite wrestler isn't suffering if they get pulled off of TV or have to sit at home nursing their knee.