New England is less religious because of the rot within the old Congregational churches, which were once the Puritans, I believe. That denomination, now the Church of Christ, is extremely left wing. The left wing politics disiplaced the preaching of the Gospel and old-time New Englanders drifted away from the church. That began long ago, probably in the 19th century. Maybe some church historian can shed some light on this.
Good point.
In earlier days, the Congregationalists (now the UCC)became too identified with political power. They were like one of Europe's established churches, and you didn't get as much evangelical fervor as in other parts of the country.
Another thing about New England is you're never that far from cities, so you don't get the large rural areas that you do in other parts of the country. The urban influence is stronger, hence the region is less religious.
Now just why one of the most rural states in New England should be the most irreligious, I don't know. It may be that you have fewer Catholics in Vermont and they assimilated more to Protestant habits.
It also may have something to do with all the "flatlanders" who moved in from elsewhere. Rural Northern Vermont is more Methodist and Baptist than Congregationalist and may be more religious.
Or maybe where it's snowy and cold, people want to stay home on Sundays.
Perhaps “now the United Church of Christ”, but most assuredly not the nondenominational group known as the church of Christ.