Not all of the mass transit in Boston is weather protected. Snow routinely causes train stoppages. The lines are also really old, being dug by hand when street cars and horse and buggy still existed. There's also the face of massive cost increases forcing people to take transit and park, not to mention the increase in commuting time by not getting directly to your location. I've been on some really great transit systems in places like Bucharest and Tokyo. Boston is an unfortunately poor comparison on some lines.