You don't know that. Usually there is less station inventory during games per hour vs. owning the entire inventory during a local sports talk show during drive times.
Maybe you're right about the station keeping all their ad inventory for local hosts. But, are the local hosts on KMVP popular enough to warrant being on every day instead of play by play? There are bigger sports stations across the country that pre-empt popular local shows for play-by-play. Why is KMVP reluctant to do so themselves, especially if they know that the PBP will attract a much larger listening audience?