The power of intimidation
Many people managed to convince themselves that Obama was a genuine, dyed-in-the-wool progressive at some point during the primaries. For no reason as far as I could tell -- his voting record in the Senate was pretty much identical to Hillary Clinton's, and the people he surrounded himself with weren't exactly "outsiders." But in the midst of the pie fights, that hardly seemed worth dwelling on for the pointless vitriolic arguments it would have engendered.
I mean, it's not like whether or not Obama was a progressive (or responsive to progressives) really mattered to the people who frequent left-wing blogs, did it? Or that the time to come to grips with that might have been back before, dare I say it, June?
Better that the mellow stayed unharshed, I say!