#2 It would be a big Payday for him

One thing that works for AEW is the foundation that it is getting built on. It's not an unreliable brand that would have to scrap for money and infrastructure. The company is not cash strapped by any means and is willing to pay the big bucks for the right talent. Right now, AEW would view CM Punk as the right talent for them and would be willing to put the money out for him.
Punk, on the other hand, hasn't had much in terms of a big payday ever since he left WWE so this is something that he would not be looking to miss out on. To add to that, the possibility of becoming a relevant figure in the market again would lead to endorsements and further financial deals. After being away from the public eye for so long, signing with AEW could give Punk a financial boost.