Is there a particular reason why I can choose who the Post Author is?
It makes close to no sense on why this option even exists.
The Post Author should be, by default, who ever is logged in making that post.
I don't know, but I think that this is slightly silly.
Who ever makes a post should really be given credit and if an editor helps that author, it still doesn't particularly change the fact that the original author still wrote that article or at least, the concept of that article. If there was an editor involved, I don't see why there isn't something that posts who Edited that Post.
This is really just me ranting at how much of the back-end I have to modify, plug-in and custom build myself just to make it behave in a semi-logical fashion.