The rest are appointed. Many of them are enormously powerful, and they are answerable only to the party establichment and/or to the person elected in the huge district back home (even tho many of them really live in the DC area).
And there is no reason why much of the decision making,
the investigating,
the law writing,
etc.
now done by unelected appiontees
couldn't be taken over by people ELECTED directly by the people.
Not qualified, you say?
Well, how about electing QUALIFIED people,
and letting THEM run the Congress?!