Dont exactly see the appeal of what someone with my login credentials would do on HN.

Doxxing. Posing as you, to get you fired or otherwise affect your reputation, especially if there is already a traceable connection to your meatworld persona. As a first step in a fraud scheme. To leverage social credibility to affect others.

The options are varied, and are really only nerfed by obscurity of both the platform and your handle in terms of its doxxability.