He's not. He wants a better situation with good NBA talent to manage, which is why he chose to not extend his contract last off season. The Jazz aren't letting Corbin go, Corbin is walking away from us.
Corbin knows how scared other coaches are of his game planning and offensive ingenuity. He knows how valuable the other franchises see him and he wants a raise he well deserves. Utah won't pay him $5,000,000 like L.A. would, so he's following the money like everyone else does.
My guess -- He'll most likely go to Minnesota and turn that into the 50+ win team they should be.