They return their funds because they are traceable, in the case of Casinos they are quick to find vulnerabilities and big casinos are good at doing that, that is why I prefer and highly recommended playing on big casinos they can do refund they have top-level security when it comes to casino security funding and financial capability is a big factor.
Well, you may be right that big casinos are more capable of detecting and tracing where their vulnerabilities being exposed and attacked on because of their higher financial capacity to acquire resources for such. However, it still doesn’t change the fact and probability that they may still get hacked, because as have been stated by the others, nothing on this world can never be hacked. I guess it is safe to a admit that vulnerabilities still do exists in every platform even in this modern era.