Probably the same reasons citizens of the city get absolutely no congressional privileges; Congressional Representatives are in an upper class that doesn’t care about the peons they perceive to be beneath them (re: the citizenry of the District). So, as D.C. has no representation, the representatives have no reason…

Personally, I’m a fan of the reversible lane on Independence on the south side of the Capitol. It’s always exciting playing chicken with tourists driving the wrong way in that lane during rush hour.