I hate to defend a major party, but it does feel like people expect Democrats to fix all the nation's problems when they have utterly no power to do so.
The reality is most Americans are not with Bernie on the things he's talking about. The average American has been heavily propagandized by the corporate media (not just news media, all of it) to love corporate stuff. Capitalism good, socialism bad, cheap gas good, electric stoves bad. Go to most Americans in the rust belt, that's how they think.
If Democrats are supposed to skip to the part where they implement policies that no one currently supports outside of liberal intellectual circles with all the power they supposedly have, that's skipping to the end. What's Bernie's solution for getting people outside of Vermont on his side to begin with?