Well there are multiple very sensible reasons to do it. (Whether those reasons actually outweigh the negatives is a different story though lol).

Given how far east Massachusetts is in the timezone, the sun rises and sets earlier here than most other parts of the country. Having enough sunlight in the morning is important to ensure kids can get to bus stops or walk to school safely. Older kids can navigate more safely with less light so they are sent in earlier. Having enough sunlight after school is also important for safe travel home and so kids can have more time to participate in after school activities that require daylight such as sports.

I think most people (at least in my experience) acknowledge its better for teens to start school later but they are unsure of how to fix the sunlight related safety issues. Installing more streetlights and lights around sports fields would be a solution but most towns don't have the money for that.