I'm not surprised. I knew he would never end up being the Dem candidate:
1. The fact that he is gay would almost certainly cost the Dems most of the black vote that they value so much, as well as the Latino vote (i.e. In 2008, when the Prop 8 gay marriage ban was on the ballot, blacks and Latinos were the racial groups who voted most heavily in favor of it).
2. The radical things he's proposed (i.e. a mandatory carbon tax on all American citizens, and the full decriminalization of most hard drugs) would not be the sorts of things most voters would support.