Well, since I didn't say that "Lavell's glory ended in 1985", I don't have to explain anything.
What I did say that the program's remarkable upward trajectory ended in 1985. Looking at the post-1985 records it is obvious that Lavell had trouble consistently replicating the success of 1979-1985 over the last half of his career. And some of those seasons in the time period you mention were stinkers (1993, 1995) that would have people here screaming for Bronco's head if they happened today.
Not to mention a three-game losing streak to the Utes, which would be a deal-breaker for many here.