92 of top 500 subreddits are moderated by 5 accounts.
Reddit moderation is practically a full-time job. It's understandable why very few people would congregate in the top reddits. The vast majority of people do not have the time or energy to dedicate that much effort into moderating an online forum. I figure once you get into it deeply enough it becomes an addiction in and of itself. I still use Reddit but only to frequent very small topic-specific reddits.
That's not the way it works. You can steer things your way for a while but everyone is looking for the conspiracy. I knew a guy who was dumping affiliate links everywhere (because everyone was innocent once) and flagrant shit like that was making him a couple hundred bucks a day. But you're discounting the deep distrust all the ad agencies and content producers have for Reddit because they lie about their metrics and consider themselves unaccountable to everyone. We ran $10k worth of advertising on Reddit once because we were true believers. And despite the fact that I had a herd of anime lovers running ads about new anime for anime lovers in /r/anime, the end result was a bunch of doxing and flamewars and DDOS of servers because, and I say this with no quaver in my voice, The Reddit demographic is utterly fucking worthless.
100% chance it happens. Those scandals happen all the time. The thing is, the money being spent is modest because the effect is modest. You're generally talking about mid-level Facebook advertisers with like $5k buys, $10k buys. If you're at all good at computer it's a shitty way to make a living because moderating on Reddit is fucking awful. You're doing it because of the somatic fame/power/dickhead hit not because of any financial influence.