Atlanta didn't really seem to be interested in giving Horford the max.
This isn't accurate. That makes it sound like Atlanta was happy to let him go, or that what they offered him was far away from what he wanted.
The negotiations reportedly came down to the wire, and for whatever reason Atlanta balked at offering the final $5 million on a 5 year deal that would've been worth well over $100 million. It's odd, really. But there's no basis for saying that the two sides were far apart, or that Atlanta didn't want to pay big bucks to bring Horford back.
I'm super thrilled that the Celts landed Horford. I didn't expect it to happen. It was a huge accomplishment for Ainge and the Celts brass that they convinced a player of Horford's stature to come to Boston. Let's not pretend it was a foregone conclusion that they'd be able to pull off a move like that.