There are many ways mist of these casinos compensate there customers or gamblers that might have had a lost of loses and in order to make them keep using the casino by not going to test other gambling platform or casinos, they can give a bonus to the player so that he can have some taste about the site generosity and try his luck one more time.
Bonuses are one way to attract customers to keep coming back to the casino and they often use this, especially if there are certain casino-related events. But for cashback, maybe not many use this method to attract customers because it means the casino returns the money the customer has lost. Maybe casinos can use the method to entice customers to continue gambling, it is probably rarely used by casinos. But whatever the type of promotion the casino does, it must be the ways that the casino can get more customers.