This is all complete speculation but there was a regime change at the very top. The previous University President saw athletics as a public relations tool to put the school on the map and parley that into increased academic prominence. I am not sure the new president sees it that way.
Second, like everyone else, there have been furloughs and other money saving cost since the pandemic, notably baseball was axed after less then a season. They had axed wrestling to make way for baseball. Wrestling was popular because it was one sport where a lot of local kids had participated and been successful. Cutting it caused an uproar and after baseball was cut, a lot of people were wondering what was going on and why wrestling was cut in the first place.
The real architect of BSU football success was actually the long term AD Gene Bleymeir, who did have a lot of vision and was really good a identifying head coaching talent. I think he hired every head coach the tree before Bryan Harsin. Bleymeir was AD for 20 years until 2011.
It is interesting to watch the changeover from Coach Pete to Bryan Harsin. Everyone in Boise loved and still loves Peterson. Despite being a local kid who played at BSU, and despite a 62-17 record as a head coach, Harsin doesn’t seem to have that same veneration from the Bronco faithful. They complain a lot more when he loses than when Peterson lost. Even though, they were 11-1 last year, there is a vibe that the glory days are somehow past. Not to say there isn’t a lot of support, it is just different. Last year, despite a really good season, I don’t think the stadium was sold out once. Typically, BYU is the largest crowd of the year when they play in Boise.