Compare it to anything else in life. Imagine if you are the owner of a shop and you only accept card payments. Why would you turn down those willing to come to your business with the intention of paying with cash? It doesn't make sense from a business perspective.
Since it's a physical shop where you already fulfill many requirements and follow the regulations, there's no reason to not add more payments.
But, cash and Bitcoin is different, any government will not question anything when you accept cash, but if you accept Bitcoin, you might need to follow certain specific rules. If the rules are harder to met/much effort than the reward, many people will refuse to add the payment.
If we relate a physical shop with a physical casino, there also the casino has to abide by the country's rule. If the crypto is not legalized, the physical casino will not allow payment in bitcoin or any other crypto and may allow traditional modes of payment like bank accounts or credit/debit cards etc.
Unlike online casinos, where it may not be easy to track and take legal action, physical casinos are more likely to be sued if they do not follow the rules and regulations of a country. Considering this, it is easier to operate an online casino as compared to a physical one.