Well, it's important to bear in mind that most of these ads supposedly didn't back or attack a particular candidate, and that banning foreign funding of political and social activism of this kind would be a very Russian thing to do. Claiming they're foreign agents is one of the Russian government's favourite tactics for raiding and shutting down inconvenient political NGOs and activists. Frankly, I wouldn't entirely put it past them to fund these ads partly to bait out something they could use to justify their own domestic crackdowns and spin US criticism as hypocrasy.