It might well be that they just prefer WWE. That they might not like the atmosphere in what, until now, has not been as structured a place. Some have blossomed, Swerve, some didn't, Andrade.
Truthfully, they all have their limitations, I think you could make a case AEW could use Buddy better but Lee is recovering from nearly dying from COVID and may never be the force he was, Black apparently has lingering injury issues and Miro is very protective over his spot.
Truth is, all of these men had their best moments under Hunter, Triple H is less likely to discard them for a new wrestler as Tony Khan seems to have a new toy syndrome thing going on, and they are gonna be playing to bigger live crowds.
If I'm honest, I don't think they will be used any better in WWE, but I can definitely see why they may be making eyes there.
I think it some cases it is fair to want to go back, but the way they've gone about it is in many cases not great. Nevermind a lot of them angling for a move after signing new big contracts after their initial AEW deals because HHH made moves asking them to break out of them. That and the fact it seems pretty obvious a number of these guys saw it as a golden parachute and they are actually above it as a company.
Andrade frankly went about things disgracefully - making heat and then punching Sammy Guevara a week after Kingston got done for the same thing, just to get out his deal. And then after Tony probably incorrectly tried to integrate him into Collision and the C2, goes out on bad terms. Punk did some shit, but even his stuff didn't seem as overtly pre-determined as Andrade
Black is either legitimately hot a fucked back, or is got a Coutinho's bad back. What I would say is (and Brit wres Twitter rumours so massive pinch of salt) is he apparently had the reputation of being Tommy (Bell)End in his old Brit Indy days, and had a comparison akin to the old Dutch national team dressing rooms at major tournaments.
Keith Lee I honestly don't know, the timing around the Swerve match cancellation is suspect but may be completely legitimate as COVID fucked him badly.
Buddy hasn't done much, but then again I don't think he was really worth the signing - not good or big enough to be better than your own roster, would have been better in TNA and being a top guy there IMHO
And Miro is Miro - he doesn't get matches as he refuses to job to anyone not ex WWE.
And to be fair, for all these possible types, you get a Cody Rhodes, a Shawn Spears, a Jade Cargill (not an ex WWE but someone who jumped) - goes out properly with no animosity and generally everyone happy for everyone either way