There are lots of assumptions, such as that the betting market is liquid enough, that the betting market is consistent with the strong efficient market hypothesis, and that bettors are sensitive to opportunities to the half point on lines. In addition, you would have to figure out how to measure bias based on fan betting population, since you would have to have a baseline and not just raw average. Is the right comparison to how computers rank the team? Relative to the fan size of the opponent? Lots of confounding variables as well, especially since the entire market underwent an upheaval in 2018, and still is not a free flowing market because of state-level restrictions and competition between gambling services (compared to, for example, the NYSE).

Again, I have done none of that work, and don't intend to. But I just find it comical that CBers are so sure that the betting markets are perfectly reflective of what the general public or institutional bettors or whatever (different posters use different baselines) without doing any of the work. It is certainly possible that the fact that BYU fans generally don't bet on their team is reflected in the lines. It is also possible that it does not. But everyone here is just asserting one or the other as true.