Like most liberal/Dem leaning areas, much of the answer can be summarized in two words: social issues.
Plus, it's in Massachsuetts, one of the most (if not the most) liberal state in America.
Democratic Single-Issue-type voters seem to be approaching the same amount of clout that Republican Single-Issue-type voters have had since at least 1992 and definitely by 2000. These type of LGBT and Planned Parenthood-style voters probably devisively swung Nevada, Colorado (where exit polls showed that the average voter was pretty neoliberal) and maybe New Hampshire the same way the Evangelical vote may have swung Ohio in 2004.
