#2 Brock Lesnar is a prizefighter
As I'd noted earlier, Brock Lesnar has gained a considerable amount of notoriety for being a master manipulator in the world of contract negotiations. The man has played the UFC and WWE against each other on several occasions and has almost always managed to come out of the negotiation wars, with multimillion-dollar contracts for himself.
At the end of the day, Lesnar is a prizefighter. He performs for money, and has time and again emphasized -- even in out-of-character interviews with the MMA media -- that he really doesn't care if he works for WWE or the UFC. Lesnar has made it a point to notify everyone in the sports and entertainment industry that all he cares about is how much he's paid.
Now, while Vince McMahon is surely capable of competing with Shad Khan -- should a bidding war break out between WWE and AEW over Lesnar -- it's a well-known fact that the WWE already has several talented wrestlers signed to its roster. The WWE doesn't really need Lesnar right now, whereas AEW could use The Beast as one of its top stars...