Anonymity and popularity of Cryptocurrency are two of it's the best attraction.
And Cryptocurrency games are more transparent.
Will, there comes a time that all online gambling sites will be Cryptocurrency based?
Crypto-based gambling sites are still behind in the competition. Sites like Bet365 have over 35 million users whereas biggest of the crypto-based gambling sites have at max like 1M users.
But the thing is crypto gambling is much more anonymous and non-traceable. These features surely attracting more and more people towards crypto gambling. The only condition when all online gambling sites start using cryptocurrency is when users demand for that.
Consumer is the king! As far as users are ok with fiat gambling, I don't see any reason why sites like Bet365 will switch to crypto.
Gradually the numbers of crypto based gambling sites is increasing although they have not meet up to sites like Bet365 as you rightly said however as the numbers of cryptos users and enthusiast increased more gamblers will divert to crypto based sites based on it anonymity while the compulsory KYC for fiat based gambling sites is quite discouraging and shelving new gamblers switch over to crypto based ones.