Hidden city tickets are weird because if the cost of flying A to B to C is lower than A to B, that implies the cost of flying B to C is negative.
Does the government pay airlines to fly to podunk towns that wouldn't otherwise get service, or something?
Why don't they just make that leg of the flight $50, but hand out $150 to everyone who's actually on board mid-flight? That would prevent people from booking the flight but not taking it.