Naw it's not because they feel guilt. They don't want the child to cry. They like the idea that their child gets to go nuts and act horrible because deep down inside them they wish they could do that too. They are quite comfortable with letting their kid get their bad bahviour on in your house because they pay you and you WILL put up with it or not get the money. They also feel their child should have their way and not be upset at all. Their kid deserves that because he/she is special and they are the child of their parents.
It's a combination of a lot of things but guilt isn't even on the radar.