I've been lurking there for years and still don't have one.

Sometimes I'd like to correct misinformation about something niche that I happen to be over-knowledgable about, or drop a 1-5 line code fix for the very thing they're talking about.

But if the cost of me getting that commenting access is also lowering the threshold needed for anyone (or anything) to comment, I'd rather keep the threshold high.

A good chunk of users on lobste.rs are bloggers, so if they get something not quite right, I can just contact them through their blog anyway.