They never had any tangible support among mainstream Democrats, even of the progressive faction, so they had nothing to lose there; the only thing they had to lose—and contrary to your claims they did lose some (but not all, the left fringe isn't a unitary hive mind) was on the left fringe. I suppose you are probably mistaking concern for the content of the early leaks with support for Wikileaks, but those aren't even approximately the same thing.