I'm convinced Vegas opening lines, when set, are heavily factoring in a teams' recruiting analytics for their personnel
It would make sense for them to lean heavily on that data early in the season, along with returning starters and such and the models likely continue to use that data heavily throughout the season, while introducing new data points for results.
This is the only logical explanation why BYU keeps having unfavorable (or favorable for motivational purposes) opening lines.
BYU's low recruiting ratings for their personnel would drive low confidence in the models