Many of them did go to New Hampshire, Maine, and Upstate New York, which is part of the reason those areas tend to vote Democratic. I'm not really sure why Vermont got so many, though. Maybe because it's equidistant from Boston and New York, so it got a lot of people from both of those places?
It had the lowest population of people already there, so the newcomers formed proportionately the largest share of the population. And once it started getting a reputation as a liberal state it became a self-fulfilling prophecy, attracting liberals to move there.
