I personally think that the cashback system plays the most important role for a casino site nowadays. Because almost all gamblers lose their bet at some point of time while playing gambling, in this case gamblers will be most attracted to the site if they are given some percentage cashback of their loss amount. i think this is a potential strategy. Because I myself personally look for such sites
In fact not many bitcoin casino offers cashback, most bitcoin casino offers rakeback. I myself prefer to have rakeback than cashback, because rakeback gives players something back based on the wagering activity regardless how is the overall profit. It means that losing and winning players will still get something back. Cashback might be something attractive for whales but for small player like me, the amount of cashback wont be big since I wont lose big amount of money, that's why rakeback is a better one than cashback.
Not many casino sites offer cashback because it can be a unique facility but it is very costly so casino sites don't agree to do it but if a casino site has a high budget for marketing then they can try it. Personally I think it will work very well. Because when a person loses in gambling he goes into a kind of depression but at that time if the casino site gives him some amount of cashback then he will be able to overcome that depression and he will be more attracted to that site.