Would have rather had Sully for one year at $8 million but perhaps he wanted a change of scenery (or we did).
It's not about $8M this year, it's about next year. He'd taken the $8M here easily I'd think, but probably didn't care for a non-guaranteed contract next year (and probably didn't care for the risk of playing at that money also).
Who knows, but I feel like this type of contact was offered to Sully first. He clearly out played Zeller, plus his cap hold was lower, so with that in mind I'm sure he was Ainge's first choice for this type of deal with no future commitments.
Now if the choice was for a longer commitment, I think Zeller would've been Ainge's guy most probably. In the end Zeller remained regardless.