This is the case with almost all demo games that you can find at different cryptocasinos. Imagine you try a game and lose 3 times in a row... the probability is very low that you will try the game with real money. Whether it must be that very high winnings are displayed in the demo games is of course questionable, but I understand the casinos that here the outcome of the demo games is mostly scripted.

The games are only meant to help you get to know them and have fun with them right away. You definitely have fun when you see winnings - at least I do