AEW appeals to an anti-WWE "s"mark audience.
Bryan and Punk were perfect signings cause they both got over against WWE's best efforts. Punk walking basically made him a folk hero for people who resent WWE.
I don't see what Punk has to offer WWE's fanbase of elderly marks and families.
Even if Punk wanted to go back, WWE is a publicly traded company they can't risk him going off like this again.