Because it is easier to create slapstick than meaning.

Humor may be a part of life and discourse, but in certain cases, and especially on the internet, it distracts from the real issue at hand, as most slapstick fails to convey meaning. If you can make me laugh and then think, then more power and karma to you, but most of us are unable to produce such witty insight on the fly all the time. We try. We fail, and we spam. That's why HN doesn't like slapstick jokes. If one person starts using slapstick then it creates a chain reaction that distracts from the real issue at hand.

Such slapstick doesn't create meaning. It ends up destroying it.

I hope that made the issue clear to you.

The initial criticism and long discussion any time someone cracks a joke isn't much of an improvement.

Except that it at least prevents the discussion devolving into a long chain of jokes, like you see on Reddit, and generally keeps this kind of thing to a minimum overall on HN.

There's a place for those chains of jokes, and that's mostly on Reddit (which I enjoy browsing often). But I would prefer to keep the discussion here on HN a bit more meaningful.

I think mkr-hn's point, though, is that Reddit may have joke chains, but HN has "tell-people-why-they-should-not-joke" chains. They're probably both equally time-wasting (this whole thread is a good example, and yes I'm aware of the irony of adding to it. Shit happens.)

Ah, but we also have threads with neither, or threads where the jokes have simply plonked to the bottom of the page with no discussion.

Linking one of my other replies in this subthread is better than trying to come up with a unique answer: http://news.ycombinator.com/item?id=2865270

I don't want to speak for him, but I'll give my opinion of why:

Reddit tends to be overrun with memes and jokes, and HN has always been more about lively discussion and facts. Reddit used to be like that a couple of years ago.

HN is allergic to humor. It's not entirely unfounded, but sometimes people take it too far.

It's not allergic; jokes are just off-topic here.

I like good jokes, but when I want some, I go to bash.org or the like ('Humour' folder in my GReader has more feeds than 'Technology'); but HN is not for jokes, it's for good discussion, so let's keep it like this.

I find that HN's comment policies seem much more relaxed on the weekends.

I find HN's comment quality relaxes on the weekends too.

I find that HN's post quality relaxes on the weekends, too. ;-)

There seem to be a lot more reposts and borderline-spammy self-promotion or poorly disguised press releases.