There is something I don't see other people talking about that likely contributes to this.
I don't want to put my username out there and let people associate me with this username. Many people do, but I don't, and I suspect many other people don't. In fact, this is a throwaway account -- I think the 4th HN account I have. That said, I very much would like to connect with other people offline with my real name.
Why? I have a lot of experience, I read a ton of things on HN and other places and have a lot of knowledge of many things. But I also have strong opinions that other people don't agree with, and may occasionally write those opinions in a not-so-nice way. (I don't find that necessarily a problem -- that is what Internet is for, and I should have a bit more freedom than what I say or how I say things at my company, especially criticism). In addition, I do want to hide my identity here, so that people don't dox me when they don't like what I said (I can guarantee you that happened), or people who know me IRL can associate me with this account based on things that I say.
I share a lot of knowledge in my comments, and run knowledge sessions at my company. I would love to network with people. But I don't see myself signing up on meet.hn -- I'll go with meetup.