The games are setup to take a percentage. It varies with the game. Slots are some of the worst, IIRC the house take is 10%. Pai Gow poker (depending on house commission and exact rules) is 1%-3%.
If you make bets commiserate with the size of your gambling budget then your expected loss over the long term for slots is 10%. Your expected loss for Pai Gow is 1%-3%.
If you make larger bets than you should given your bankroll or play bad strategies you can lose a lot more. If you get lucky and quit immediately after a big win you can come out ahead.
The house doesn't give a fig if the average person loses or wins; they just need people to play. They are well aware a significant number of people will walk away winners and that makes them happy: it's great marketing!