Massachusetts went for Humphrey by a big margin relative to his performance nationwide in 1968. So it might just be an effect of JFK's lasting legacy(first catholic, from massachusetts, people still remembering him after he was assassinated)
Maybe because the people blamed Nixon / Republicans for so many textile jobs leaving MA and heading south. In 1972 the unemployment rate in MA was more than a full percentage point above the national average. This may explain why Boston's working class areas went for McGovern: South Boston, by 63%-37%, Somerville, by 67%-33%, Waltham, by 56%-44%, and Lowell, by 60%-39%-- areas that in any other state would be Silent Majority communities for Nixon.
https://fred.stlouisfed.org/series/rinan#0https://fred.stlouisfed.org/series/mananYea Neighboring Rhode island swung towards Nixon heavily as their economy rebounded from the early 1970s recession by late 1971, While Massachusetts only recovered by the end of 1972. Along with the JFK legacy. McGovern was able to win Massachusetts.