It's why loyalty programs exist. People who spend a lot of money on gambling look for good loyalty programs, and when they are satisfied with the casino in general and the bonuses they got from their VIP level they will stay there. When there is a better offer it's more likely that someone will change their mind.

I don't have a lot of experience with online fiat casinos when it comes to lucky-based games (including slots), but when it comes to sports betting and poker fiat casinos still have a lot more active players and better options/bonuses. I still think that crypto needs some fantastic "only crypto" poker places, but I guess we are far from that.