At least two major factors:
- Between about 1990 through about 2010, Russia collapsed, flirted with a liberalized, free society, then re-entrenched back to a totalitarian state.
During this time, Russia lacked first the means, then later the desire, to meddle in foreign affairs, for roughly twenty years.
Russia was so cordial with the West that American views shifted somewhat to seeing Russia as a peer and potential friend for the first time. For example, in the 2008 election US presidential election, one of the touchpoints was Russia; one candidate (Romney) suggested Russia was an enemy, and he paid dearly for that view in popular opinion. To the American electorate, the Cold War was over and Russia was finally a peer.
Russia has since returned to an antagonistic relationship with the West, going so far as to invade Ukraine when a Russian-friendly Prime Minister was ousted by his own party (for shooting protestors) in 2014. When they couldn't win on ideas, they decided to win with violence.
So it may look like Russian influence is new, but that's only because we had a wonderful break from Russian imperialism that lasted decades.
- Modern Interconnected World
It's a much smaller world now.
The biggest part of this is the internet. It's a lot cheaper and easier to influence populations when you can post a screed to a board seen locally from the other side of the world.
It's not hard to have an individual in Timbuktu write a question on a message board about something seemingly reasonable, and either heavily imply FUD so it gets accepted as truth (see "free trade bad" in this very question: we could argue that point for days, but instead it just gets implied here and gains market share without debate), or pushes a conversation in a direction they want (like one poster asserting Reagan shows that Democrats think we should force Ukraine to surrender).