He likes the challenge of fixing broken systems. Plus he gets time off versus year round work in in college. Sounds like his wife didn't want to make another move. That said, they were in the middle of a contract extension.
Im a pistons fan but it would be a horrible job to take. The entire team salary is tied up in reggie Jackson, andre drummond and blake Griffin. If he wants to coach in the nba wait for a team thats young and/or has money to spend. The pistons are going to be garbage for years.