You may not know this, but all over the air stations get funding from each cable operator for allowing those channels to be rebroadcast.
So watching broadcast FOX on cable does boost that channel’s income from mandated fees.
So Fox gets paid two ways - first for running the ad and then from the cable company.
If Steyer is a fool for spending his money then anybody who watches Fox on cable is a fool too. You’re paying to watch a stupid ad.