where are all the hacker biologists, psychiatrists, or gardeners?Err, we are here. You'd be wrong if you thought that everyone in HN is a startup person, or even a programmer.
However, this is hacker news hosted on ycombinator.com. There is a prevailing standard focused on startups and even though I am not one of those people (nor do I wish to be), I do my bit to fit in with the community standard.
It's like you are walking in a park and there's a bunch of people having an interesting conversation. You might ask to join in, but saying "why don't you people have an interesting conversation about clock mechanisms instead?" would be kinda rude.
Saying "I love HN, but sometimes I wish it wasn't so obsessively focused on tech and start-ups" strikes me as saying "I love the San Francisco Symphony Orchestra but I wish it wasn't so obsessively focused on classical music".
[Later edits in light of comments below:]
The interesting question to ask is "why are the non-startup people here". I can only answer for myself: I came here to pick up interesting new sites (in that way I am a refugee from techcrunch - reading it felt too much like a lobotomy ). I stayed because of the quality of the discussion and because even though the startup folks sometimes seem to think they have a unique ecosystem, a lot of their issues are really common to software and even wider technical groups outside the commercial sector, like my own.
So no, from that point of view I wouldn't go to an HN fork - I just can't afford another time sink, and I would still need to be on HN for my tech news.
As for non-software stories, there are quite a lot of really interesting stories submitted, but they often don't gain enough traction for the home page. But there is a lot of really varied stuff in /new if you look.