So it that why the state leans progressive? Liberal transplants from Boston? For a state that seems to be mostly rural without a large city, it is amazing Bernie Sanders is the senator.
Vermonter here. The average Vermonter voted for a Socialist Senator, a Democratic Representative, and a Republican governor in the last election. The person tends to be much more important than the party.
Vermont was reliably Republican until there was the perception that the GOP had an evangelical social agenda. Vermonters are not against private expressions of faith, but they believe it is deeply personal and have no interest in being lectured on it by politicians.
There's a lot of people from NYC that want to retire upstate but come to the realization that NYC has done a very thorough job turning the entire state into a dump and that the only way out is to move out of state.
However, as a sibling comment pointed out, even if you ignore transplants the people of Vermont tend to agree with the modern left on a certain set of social issues anyway.