As I've been saying since we stood pat at the deadline (we could have had players like Nurkic or Drummond to improve our team for assets), I think Hayward is coming here and Ainge + Stevens know it for sure. So we can't add any player who prevents us from having cap space.
And that's why we traded down as soon as the front office learned the salary cap was lowered to 99 million.
At least, that's my theory. We must admit Butler was cheap in this trade and we could have gotten him, but I prefer Tatum+Hayward to Butler. This also makes Crowder expendable to be traded and get another asset or go all-in looking at Porzingis.