Because, given the opportunity, some people will abuse the system in their own failure to grasp how communication works:
Can we make this infractable?
What I'm specifically referring to is a user going through their posts in discussions, and wiping or deleting them, after they've clearly had enough time to stand and sometimes have already been responded to.
(Obviously this wouldn't apply to say... accidental duplicate posts, or art posts, or whatever, since those come with implied ownership on the part of user.)
It just seems like a very cheap and immature way to try to circumvent responsibility for what one says in the public space,
and is largely detrimental to discussion as a whole, if someone just goes "NUH-UH! I DIDN'T DO THAT!" and just starts blanking things.
I know FAF had a similar policy, or at least a similar policy as it applied to blanking the OP of a thread after said user got called out on making that thread,
so I don't see why that would be out of place here.