because BYU fans don't bet as much as other fans, you would generally see a trend where BYU beat the spread more often than not, which would in turn cause the serious betters to realize that betting on BYU consistently was a good way to win their bets, which would in turn move the line towards BYU. Or at least that's the logic that makes sense in my line, and at the end of the day the line simply is matching what public perception is on the teams and what the "general public" thinks will happen.