There's "not having time to work on it" and then theres "complete abandonment."
I do sort of agree with OP that at least adding a few more people onto a team would be good, if not full on opensourcing it.
But hey, Reddit is always open source. And someone could always open their own site out of its source code and try to one-up HackerNews. Competition breads innovation.
On a slightly off-topic talk, I think the whole thing basically boils down to the crux. People aren't too bothered to change the looks of HN because it just works good as it is and that's most important. Now, ages from now Apple's design philosophy might look pretty old but may be people will be okay with that because it's a brand. I tend to think of HN like that.
By the way, our Hackerspace is looking for a sane, reddit-line threaded discussion engine. I'd use HN engine, but it doesn't support "subreddits". Anyone knows something that could work? We had hard time finding anything.
Particularly its useful, if I have not used HN for some days, and come back to see 'what great items have I missed?'.
edit: minor rephrase