NBA coaches make much more--it's not just the base salary.
Think of it this way... a great high school baller wants to play at the highest level D1 they can. There's a reason Clingan didn't commit to CCSU.
Same is true of coaches. Many coaches want to test their mettle against the best of the best, and coach the best of the best. And a lot of coaches end up flaming out because they couldn't hold up.
NBA is a very different game off the court. I think that piece will be the biggest adjustment for Danny.