You don't understand the internets, that's why. I've learned from the past that it's a waste of time trying to explain to you such a thing, but here's a couple examples laid out.
-Say a new person joins, they'll see you have a high post count, they'll assume you're a respected/notorious member and in most cases reliable. Yeah, I know there are some exceptions, but what I'm mainly getting at is that if you have a high postcount, they'd assume you know what you're talking about, whether or not your a jerk or use sarcasm a lot.
-Also on the UBB when we could frequently change our own names, like if someone recently changed their name, their postcount would show they're someone that's been there for a while and not someone new.
So yeah... don't act like they mean nothing. I was never competitive about postcount and I know you generally dislike the competitive aspect of certain things and choose to act like the whole thing is pointless, but at least I'm willing to admit it has a purpose.