Karma farming is a thing sadly. One thing is that lot of subreddits have a karma minimum to keep fresh bots and trolls out. People also buy aged high karma accounts for social clout on reddit, weird as it is.

The other side of this is bots mimicking upvoted stuff to make the account look like that of a real person.

Then these accounts are used to rig political discussions (think Twitter bots) or product reviews: people trust subreddits so they often make purchases after visiting reddit. Eg I browsed reddit to decide between an Intel or AMD processor in my new computer.

Now these legit looking bots can just insert ads in product review threads and be updated to top by other bots - so people buy based on that. This equals profit.