>>9956208The same reason you would sign any wrestler. You need people to work. AEW has (over)used debuting wrestlers as a gimmick since day 1. You sign him to deny your competition an asset. You sign him as a favor to people already in the company or for his relationship value. You sign him because he may be good and will get himself over.
It makes sense to sign the guy. There’s only so much room at the top of the card though. Not immediately slotting the guy at the top of the card isn’t bad booking. If he signed with WWE there is a 100 percent chance he would have debuted on NXT.