Curiosity have just gotten on some of these promotion features on some casino and that's because I actually tried one and the end result which I got wasn't what they promised so I had to ask.
That's the gambling industry, don't be tempted by various bonuses, especially welcome bonuses or deposit bonuses, I'm already full of these bonus promotions, as you said, none of them are really as expected, so play for real without expecting any bonuses, if you hope that you can multiply the bonus 10x, that's nonsense, you will be disappointed because of that.
So if you deposit and bet and you win, that's the reality, what you get won't be disappointing, but if you continue to rely on bonuses, you will definitely curse at the casino, indeed bonus tricks like that are often used by public casinos, remember, it's your real money that makeyou are happy.