I'm pretty sure PR companies are managing the content on the default subs, probably the upvotes too. There are websites where you can buy reddit upvotes. In 2016 correct the record were spending millions to game reddit and twitter. Reddit admins have never once mentioned astroturfing, which leads me to believe they are in on it.
At one point wallstreetbets had 1.4 million users active on the page. For comparison sake /r/pics usually has about 40k