Two things I think happened to make JB move to the NBA.
1) Age and Money - I think JB is getting close to retiring and has always wanted to move up the ladder. What better time than now - when he is probably about 3-4 years away from retiring. He goes to the CAVS who have no immediate expectations of winning, and are just asking him to lay the foundation for the future. This sounds a lot like management speak for - it might be better if we lose now, get guys with a good attitude, and in the meantime - get a lot of draft picks. Not to mention the key factor - the Cavs are definetley giving him a pay bump from Michigan. He was making about $3.8 million at Michigan, and I believe when Donovan left Florida for OKC, they paid him about $5 million, so safe to assume he is making in the range of $5 million for 5 years. Not a bad retirement gift for the grandkids and their eventual kids.
2) NCAA Landscape - JB has always been a guy who follows the rules, no matter what. But I think the past few years he has seen and learned that in order to compete year in and year out for NCAA championships - you got to be able to bend, and even break rules at times to succeed. And I don't think this is something he was willing to take on. Schools like Kansas, Duke, Kentucky, etc - are always at the top, but are just one false step away from NCAA sanctions. Not to mention the NCAA now wants to pay players a stipend or let them make money off their likeness - I think JB saw where the college game was heading and did not want to be a part of it.
I don't think he will have any success in the NBA in terms of wins, but I don't think that is the measure of success the Cavs are looking for. They are looking to turnover their roster in the next 3 years. During that time - they will lose a lot of games, but gain a lot of young players in terms of the draft. They are asking JB to instill the fundamentals on them, and a hard working attitude. That is harder to do with veterans in the NBA, but easier with guys just 1-2 years in the league looking to make a name for themselves. I would expect the Cavs to thank JB for his service after 3-4 years, once they have a good roster in place and look towards a more seasoned NBA coach. In their eyes - JB would have succeeded.