Likely a combination of generational changes (similar to how The South went from being part of The New Deal constituency to the conservative stronghold it is today), as well as a shift from social conservatism to a more social gospel type of Christianity during the 19th century, revolving around the abolition of slavery.
This. Massachusetts was very religious - it just was advocating from the pews a totally different style than in the 1600s and 1700s - the 1800s was a transformative century for the U.S. (and the world) and with each passing decade, MA's religious establishment grew more and more tethered to the idea of using God's word to promote social justice and fight social injustices, like slavery. I'm sure many in the MA suffrage movement were connected with local churches.
