Promo bots do not upvote random content. Authors are bidding to get the vote. So, when you see a post that received a lot of bot votes, it means that the author (or a 3rd party) actually paid all that money to bots in exchange for votes.

For some reason competition between authors is so high, that often they spend more then what they get in upvotes! Or maybe they forget that 25% of the total reward will go to curators.

This is one of the reasons, why higher curation rewards can make bots less effective.

Since authors hardly make any money by buying promo votes, the only real reason for them to do so is to bump visibility of their posts in Trending section and then receive user feedback, comments, real action.

And once again, higher curation rewards can help, as this provides higher motivation for readers to engage with content through voting and commenting.