It goes like this:
A post count is by definition a count of all the posts a person has made. Showing how many each member has leads to a certain type of member spamming like mad... think Alpha male theory: The Alpha is the top of his society. He has breeding rights. And he will viciously bitchslap anyone who threatens his position. He will do whatever it takes to keep his rivals in a non-Alpha status. They're threats to his position - to his right to spread his genes.
Basically, showing post counts clearly encourages those more primordial members to think that getting a really high post count is important and thus, to get as high a post count as they can, they spam
It really isn't that difficult to comprehend...
