The problem isn't that people are humorless– it's that when you reward people for humor (often resulting in puns and pithy one liners), after a while, people start competing to be as funny as possible– and that's all that ever rises to the top. It crowds out more deliberate, thoughtful discussion.

I love humor and comedy myself, but it makes sense to me why a discussion forum might deliberately choose to discourage it.

Have you ever gone onto a blogpost about procrastination and found the "I'll read this later" comment, and the "I'm here reading this instead of working" comment? Are those comments ever valuable?

It makes sense to downvote them to the bottom, so that people who go looking for them can find them, but the discussion is kept as fresh and relevant as possible.