But then you'd have to ask yourself this: Why do it then when the government can function just fine in around Maryland?
Because under TTL the Founding Fathers said so, and we need to follow them just as stupidly as we know slavery must be right because they said so.
More seriously... I got no practical explanation when it works in Maryland as well as it can work.
I suppose for the principal, people might like the president being "closer to the people" like Holy Roman Emperors. So they pass a law forcing the executive branch to do what the OP said.