Sometimes they can grow out of their job and need to move on to something bigger. e.g. Bill Gates got too big to run Microsoft and decided to address world hunger and other larger issues.
With regard to Dave Rose, who like all BYU coaches has the advantage of an incredible athletic base, he has done a very good job, but his hyper fast tempo offensive system without an accompanying effective half court game seems to have been refuted over the last couple of years. His chronic poor defense (i.e. anything worse than top 50 given the aspirations) may be a function of the nature of the recruits who often don't value playing defence.
But i have no doubt about Rose's leadership capacity or his knowledge. i believe he still has the passion and is committed to building an outstanding program for the long term.
Therefore, i expect significant change for the better this year on both sides of the ball. But we'll see. If BYU trends downward again this year, it would mean to me that the passion is gone. I don't believe that will happen. Rather, i expect an upside surprise, assuming good health.
Go Cougars! And let's hope the basketball heavens grant BYU that one last recruit for 2017-2018.