That is why the government can know what their people did with their money.
If some people use their money to gamble on the online casino, they will investigate and maybe apply tax to them or do something.
Using a private wallet can solve the problem of tracking by the government so they do not have to worry if the government will know what they do with their coins.
Using electrum can be another solution for people who want to keep their coin without any tracking from the others.
By using Electrum you can avoid taxes even if you do then its evading not avoiding there is a hige difference between that. Using Electrum can avoid the account getting frozen but if the casinos also against the country where you are living and the prohibited users then its don't gamble at all.