Beilein makes more sense for a young rebuilding roster than a team of experienced vets. I am okay with him as our next coach, but we are better off with Casey if we are going to try to win next season, which is almost certainly the case.
He probably sensed that the Pistons were more interested in Casey, then received the contract he had been looking for from UofM and decided to take the safe deal rather than the risk of losing recruits while spending who knows how long trying to interview for the Pistons job.
I suspect we either announce the GM and coach at the same time, or we announce the GM first.