I think that's true of just about every program. Bronco, for example, wanted his players going right up to the line and would rather have them occasionally go too far rather than not be at that line.
So that's part of the reason for the rep.
Another part is that BYU is widely disliked just because they've always been the big dog in whatever conference they've been in. Even in the last decade of the MWC (when BYU was probably #3 behind TCU and Utah), they were in that triumvirate of dominant teams and it's a lot easier to hate the Yankees than it is to hate the Pirates or the Royals.