He could cost more money, he could walk, the Hawks could prematurely hand an 8 year extension to a guy without him having been worth it and getting stuck with a bad deal, Levshunov could refuse to sign a relatively cheap 8 year extension and end up asking for a bridge which really presses the issue at the end of it (overpay or lose the player who has room to force his way out then). Team control is the most valuable you get from drafting a player so I wouldn't just give it up without a good reason.