Can't really blame them. The right won't vote for him because he's a socialist. The left might not vote for him because he's an old white male and not a democrat (which might make him an extremist xenophobic racist by their standards). The socialists might not vote for him because in a couple more years they'll have a young energetic female socialist to vote for who may be even further left than he is and has a very significant social media following. Why sign up for a losing proposition?
From what I noticed, people who support the socialist party are the people who prefer to 1. To not work and live on other people's money. 2. Prefer to receive more than giving. 3. Envy the rich, and want to bring them down to their level. I am not surprised why there are so many socialist supporters especially among millennials. The are lazy, they can't compete and they feel entitled.