Absolutely right, because only very keen gamblers will go looking for how to bypass the bans - they will start using VPN to start playing in online casinos in other countries. But the influx of new gamblers will decrease, and of course, guests of the country will not become new gamblers either.
In order for the casino to attract new players, advertising is necessary. But if gambling is prohibited in the country, then advertising of such services will be prohibited accordingly. This is exactly what governments are pursuing in order to reduce gambling addiction among their citizens.