Gain reputation, use the account to manipulate us at a later time. HN is a high value target for the same regimes that use Reddit and other social media platforms to manipulate the US and Europe.
We know nation states try to compromise social media platforms and Github; that isn't conspiracy, it's fact. Now whether this particular set of users serve that purpose, I cannot know. But why else would someone use a bot on this site, other than to gain reputation for the purpose of manipulation of some sort?
It is a certainty that you do interact with malicious actors representing hostile nation states on any large platform - HN is well beyond the size where it's an issue. I hope the HN team has some tools to detect and counter it, but given their small team size they probably can't do much.