I think most of the people are already using crypto for gambling. At least those who know about cryptocurrencies use crypto for gambling. It is only those who do not know about crypto that are still gambling with fiat money. Or maybe the gambling casino where they gamble do not offer crypto payments and therefore the only option for them is to gamble with fiat. Also, the bookies who operate offline still use the local currency as the mode of payment.
Some gamblers who had funds on their e-wallet instead of buying cryptocurrency to deposit opted to deposit directly.
Some e-wallets in our country charge as high as a $15 transaction fee on cryptocurrency, whereas their e-wallets offer almost free transactions. For convenience and to avoid higher transaction fees, users opt for their fiat-based e-wallet.
Crypto gambling is good but from my personal experience fiat deposit is good for me. It is less in transaction fee but in crypto deposit most people have their coins in exchange and the transaction fee to a casino is unbearable. And the best way to enjoy transaction to a casino is from non custodial wallet which the fee might be less. And another disadvantage us that the particular cryptocurrency you might have in your wallet might not be listed in the accepted deposit currency.
And that is why those casinos like 1win which accept fiat as part of their deposit currency have more chances over only crypto casinos.
Fiat currency works well for small deposits, for example, in my country, the use of mobile financial services (MFS) is very high and casinos that offer the option to deposit fiat money can easily deposit and withdraw through MFS, where the fees are very low. However, even with such a system, gambling is illegal in my country, so if we can enjoy gambling using crypto, it will keep us away from many problems and we can enjoy gambling without any hassle. That's why I always prefer crypto casinos and deposit BNB or USDT through BSC chain there are very cheap transaction fee ans also free transaction in many platform.