Here is one theory.
At Central Michigan, I don't think CBJ waited that long. Dan LaFauer or whatever was his main guy Soph, Junior, and Senior years.
When he took over Cincy, Zach Collaros (junior) was named the QB as early as April. He competing with another junior, Chazz Anderson but Collaros got the nod because Butch said he had better leadership skills and understood the playbook better. That was the first year.
He second year, Collaros was starter early and the competition was for 2nd place. (Munchie, Kay, and Anderson.)
Each time, CBJ talked about how Collaros understood the playbook much easier.
His third year, it was between Munchie and Kay and all knew the playbook (or should). but Because Collaros got hurt, Munchie had more experience. But still CBJ didn't announce Munchie as starter until late August.
Each time he went to a new school he has been able to recruit better QB's. From my understanding Munchie and Dobbs are really the only ones they have recruited.
My gut theory is that CBJ doesn't actually like competition but because he has moved up the ladder he has QB's that are more SKILLED, can understand the playbook FASTER, and all can have those LEADERSHIP skills he wants. I think CBJ is not used to that so the decision is harder for him. Basically I don't think they can evaluate QB's that well. When every QB is the same to you than you can't pick up the little tiny flaws they have. That scares me.