BECAUSE OF SOME INTERESTING HISTORICAL REASONS. THE WORRY UNDER THE *ARTICLES OF CONFEDERATION* WAS THAT STATES COULD RECALL CONGRESS CRITTERS LIKE SOVEREIGNS RECALL AMBASSADORS. THE NEW *CONSTITUTION* DID NOT WANT TO GIVE STATES THAT MUCH CONTROL OVER INDIVIDUAL FEDERAL OFFICERS.
I think it's simply because Article I of the Constitution makes no provision for a recall of an elected Congressperson, but specifically provides for expulsion.
I mean I know, but it makes no sense to me that that's the way it was devised. Voters elect the representative, but only other members of Congress can get them out before the next election? It feels wrong.
Oh, sorry. I'm a little too literal this morning. I agree it seems wrong but I wonder if the Founding Dads didn't believe the unwashed masses would un-elect someone they had so recently elected, being easily swayed common folk and all. I'm only partially kidding.