Reality Check
Keepin' it 100
In the United States, it's much easier to sell "elite" wrestling than "Japanese" wrestling. The mainstream wrestling community is ready for a new canon.
AEW has a deal with NJPW, who has already been promoting the company. This will allow for excursions and talent exchange. They're also paying Meltzer to keep it kayfabe. He could spill a lot more, privy to tons, but he is literally on their payroll.
Kenny will have a founder's deal that will see him capable of making more money than if he just took a WWE contract, a franchise building legacy that elevates him into living legend, and he'll work with people he has voluntarily and happily worked with for years.
And oh my god people, you do not do the "refused the countout victory" angle in one's last match in NJPW, of all places. He pulled Tana back into Ace position, created worldwide buzz, and is sitting comfortably amidst the maelstrom.
To add on to that founders/executive deal, he'd probably have complete, if not a good chunk of creative control over what happens with his character. Same can't be said for him going to WWE.