The more generous their policies on rake back, cash back are, the more money they will have to spend to users. It's more costly for them, but as a business, if they can satisfy customers, customers will be very more likely stay with them.
Casinos might have different strategies. But rewarding a little extra bonus is not a loss for the business. They will always get a good return if they do this as an investment. To make players loyal, the casinos should always provide something exciting so their players continue to play on their platform. I believe you know why people try different casinos, they look for something exciting and sometimes for bonuses. But if a casino continues to reward their players, they are likely to become loyal to that platform. I don't consider bonuses as expenses, I think it's an investment for the casino. Because they are going to get a return in the future.
That's beneficial for them if they frequently do that since for sure they can gain loyal costumer especially those people will get happy with those bonus rewards they give to them.
If they could able make people happy with those rewards they offer and frequently add more things that can raise up more their excitement while playing on their casino then for sure that they could get lots of players around. Also its better if they monitor around what's happening on other big casinos so that they would get an idea on other marketing approach they could do so that people would see new more exciting things from them.