The sanctions are nothing to them.
They've already made their own rule for the countries that they're dealing with and it's in favor of them. So all of the people that boycotts them or not, they won't care.
You decide if all casinos based on Russia will be boycotted by you or you don't do anything as that doesn't concern you and they're just businesses that are residing there and as well as affected by the war.
Economic sanctions alone are not effective, let alone boycott gambling sites originating from Russia, it is even more ineffective.
sanctions will be effective if the country that is subject to sanctions, has weaknesses (depending on other countries) while so far the boycott and sanctions imposed on Russia are not effective at all because they know that foreign countries need their gas and oil.