I think one good reason is that HN is ugly: it scares away the people I would want scared away if I were HN. It's also not very user friendly - a couple very clever friends of mine find the UI somewhat confusing. They see bug, I see feature.
But I must confess a tiny little bit of shady conduct: I tried to engineer my karma to get exactly 1337 points (slowing down posts when getting close and, once it passed, trying to lower it through a variety of tactics, from light trolling to plainly asking to be downvoted - without much success, I must add). I couldn't get a screenshot at the right moment and the best I have is a 1338.
Right now, I have 1402, which was a nice card reader made my IBM to accompany its much more interesting 1401 computer. I have a screenshot to prove.
I will try again on 3278 (the first mainframe terminal I used), 4341 (the mainframe it was attached to) and 6502 (my most beloved micro-processor). Prime palindromes may also interest me, as scaled/rounded physical or math constants. sqrt(2) * 1000 is very close. 2718, 3142... What's the first prime number after 1402?
I will consider other "karma sightseeing" ideas, so, if anyone wants to suggest some, please, feel free.
From time to time I also post my own blog entries here, as the crowd HN attracts a tad more interesting than my regular "oops-wrong-page-get-me-outa-here" readers, and so are the discussions. I will probably touch up one tomorrow and post it here. Maybe a second one (about my karma engineering experiences), if I get to write it. I gather they tend to be of high quality too like http://news.ycombinator.com/item?id=726922, that generated some interesting discussion.
Other submissions, like http://news.ycombinator.com/item?id=743423 end up forgotten. And that one is even unfair, because David Alan Grier's podcast is most outstanding.