The simple answer to this question is that slot games are designed in a way that they pay out less than players bet in the long run.
Imagine a simple game: you give me €1 and flip a coin. If you get heads, I’ll give you €1.50 back. If you get tails, you lose. It’s quite obvious that the chances are on my side. You can win if you are lucky and play only a few rounds, but I have a clear advantage in the long run. The randomness of this game is fair, but the long-term chances aren’t.
Slots are similar, just much more complicated. The math of a slot game is defined by:
- sets of symbols on virtual reels;
- win sizes in the paytable;
- rules and probabilities of all bonus features;
- settings of all bonus features.
Game math combined with fair random numbers gives the casino a long-term advantage over players. And that is how casinos make money.