I assume all of these sites are illegal in Russia since online gambling is illegal. Unless they're legitimate, tax paying Russian businesses that only offer their services to players outside of Russia (which I don't think they are), you're actually doing Putin a favor by boycotting them. (I'm not saying you should play at them to spite Putin though, several of them are outright scam casinos or very shady at best...)
From what I understand, the goal of this boycott is to ensure that the tax money does not go into the budget allocated to supporting the war.
In fact, gambling is officially illegal in Russia, but as I know companies can operate there if they have government license. Also it is possible that there may be operate companies that offer such services outside.