There are even many people who are anti-crypto, don't want to use cryptocurrency. And we cannot force these people to use crypto. So
I think there will always be fiat based online gambling sites, if in the future crypto-based online gambling sites will be more numerous
versus fiat based is still possible.
If the fiat-based casino is aware of the presence of cryptocurrency, the owner will find out what cryptocurrency is before they add the crypto on the payment processor. Perhaps, if the owner can know what the crypto function, the owner will soon add new features, and they will notice to their members that they have a new payment processor. As long as the sound of cryptocurrency can spread in many places, soon, the fiat-based casino will use crypto too. If that happens, we will see the cryptocurrency explode, and there will be an increase in the gambling industry.