Actually, that is one of the things I rather like about HN. The "loss" is built in: after a couple of days, nobody is going to read or respond to any of my comments. Everything I write here will effectively disappear several days from now. And that, somehow, is very refreshing: I don't have to worry about posterity or the future.
HN is my way of indulging in the present. No plans, no worries, no future. Very relaxing.
It's also a way of tricking myself to write. In high school, I never liked writing much and, consequently, was never much of a writer. Now I like it more; hopefully my writing improves correspondingly. HN is obviously no way to become a writer, but that is not my goal: I just want to be able to write clearly, nothing more, nothing less.
If I was doing something more lasting, I would not want to trust a single entity. This is why all my code on GitHub is also backed up at home with the most important projects also backed up on my school account: losing that would actually be painful. Losing my comment history here? Trivial.