HN's prime directive is "anything that gratifies one's intellectual curiosity": <https://news.ycombinator.com/newsguidelines.html> and many, many, many dang comments.

I'm pretty sure that the specific gripe is posting excessively (not even necessarily exclusively) on a single topic or theme. See <https://news.ycombinator.com/item?id=19392902> for a more detailed comment from dang.

Occasional alts are explicitly permitted, though not to engage in abuse (e.g., mutual admiration societies, sock-puppetry). See: <https://news.ycombinator.com/item?id=9963551> <https://news.ycombinator.com/item?id=9823379> (both against sock puppetry) and <https://news.ycombinator.com/item?id=9122086> and <https://news.ycombinator.com/item?id=7504621> (on where throwaways are/aren't permitted).

Where HN does favour persistent accounts the stated claim is to foster community, rather than for nefarious tracking purposes: <https://news.ycombinator.com/item?id=18082346> and <https://news.ycombinator.com/newsguidelines.html>. From that last:

Throwaway accounts are ok for sensitive information, but please don't create accounts routinely. HN is a community—users should have an identity that others can relate to.