What might be the motivation for upvote farming on HN? There is the personal satisfaction of a carefully written comment being acknowledged and validated, but otherwise?

You do get some minimal upgrades with enough karma, like the ability to downvote. But it's not like you get any priority or special treatment, and the numbers are not exposed unless you open individual profiles.

I suppose it could be useful to give legitimacy to bot accounts to be able to inflate upvotes of some posts, but from what I've seen vote-ring detection is really good on HN.