As I first posted it is about money but when you have 8 main ghosts and several other that aren't main ghosts plus the other characters from Jay and Sams family, construction workers, guests etc....it is hard to find a place for every main ghost and the side benefit is the money saved when you don't have to pay them for every episode. Plus the longer the show runs those people are going to want more money. It is ALWAYS about money in the long run.