They're signing guys who's contracts (and accompanying non-compete) have expired.So how is AEW allowed to essentially sign anyone? Is it because they allow their wrestlers to wrestle for other programs?
Guys are choosing to go to AEW because of the money, lighter travel schedule and more creative control over their characters and storylines.
Being able to wrestle for other promotions is another bonus for the talent, but that's gonna bite Tony Khan in the ass at some point once one of his guys gets injured wrestling a weekend spot show in another promotion.