Because taking money away from gambling simply makes the game not worth playing.
Will you still participate if money is not involved? Many people will easily quit if all casinos are to be turned into no-money games, isn't it?
It depends on how to treat gambling, people gamble because they want to have fun's gambling real purpose is, to give entertainment to the players, but few of them treat gambling as one of the possible sources of income because in just a single game you can hit a hundred or thousand multiplier that's why they take it more seriously, but if you are just a casual gambler want to have fun without having the bet i guess still ideal to you to play a game without money involve just pure fun. Money is just additional to make the game more spicy.