I think that to generate activity and make the post go viral
Mind you, I'm not claiming that's what's actually going on. But that could be the intent.
Then again I suppose the bots could also be upvoting, but I would assume that would be detectable to the voting ring detectors.
I don't know. Hacker News is supposed to be a place where human beings enjoy each other's company and conversation about common interests and intellectual pursuits but it seems like a lot of people here want to optimize the humanity out entirely.