Censure was a lesser punishment than impeachment. Once Clinton was impeached, the issue of censure was moot.
Impeachement scared the MoveOn folks because they did not want Bill Clinton removed from office. They CLAIMED that he needed to be rebuked with censure, that what he had done was gravely serious.
There was as much a legal provision for Bill Clinton's censure after impeachement as there was before (that is to say, NO legal provision for it).