An expiring guy you probably can't resign likely isnt worth a first rounder. Typically teams will make up the difference in value by having the acquiring team dump salary (Like the Mirotic trade), that boosts the value and makes the first worth it. Problem is we have no bad salary to offload, every guy we have is an asset. So if Ainge doesn't view Evans as worth a first its hard to bridge that gap. If any other team (besides Warriors and Rockets) offers a first, they beat our offer. One downside of being good. Hard to thread the value needle on Evans by offering more than everyone else, but not more than he's worth.