Since when does Fox have regular season primetime college football?
Since this year. They basically cut their law enforcement shows, Cops and America's Most Wanted that used to be in the 8pm slot because they want to start competing directly with Disney and NBC for primetime football now. - they also are looking to start a new network to directly compete with ESPN, NBC Sports and CBS Sports above what FSN does.
Which is great for Pac 12 and Big 10 since Fox has a financial stake in those conferences the way ESPN does with the SEC and Texas and thus will likely give them favorable coverage.
I think they are doing 12 primetime games this year, and so far every game Fox has announced for that slot features a Pac 12 or Big Ten team - or both.