I think that's the main reason why it's not. It's fine as it is. The minimal features list and quirky HTML is part of HN identity.
There was a question recently, about why you don’t improve the HTML of HN, where you said "When the HTML is the most important thing to work on."(http://news.ycombinator.com/item?id=4927231)
I agree that the markup is relatively unimportant compared to features that I think could really improve the functionality and quality of the site, and I bet you have a long wishlist of features yourself.
But between the lines I interpreted that that list might be way longer, than the time that is available to you, allows you to work on it.
So why don’t you open source HN? I get that with a project that is important to someone, it’s hard to give away control. But you can still be the project lead, you could still have the last call and I feel to open up the project will lead to great feature discussions and ultimately a better hn.
Have you ever considered open sourcing it? And what’s the thought process on your decision?