Because he is only a Congressman and he was hurting them by generating bad PR plus the bad PR could, and probably will now, go on for a long time with no end in sight.
Clinton was hurting them with bad PR, too, but also was President with huge abilities to help them out in countless ways, as well. Condit didn't have that benefit.
A single Congressman is rarely that important to any party unless he/she is Speaker of the House or from a district that's really crucial for some reason. Most Congressmen by far are just not that high on the DC totem pole.