They benefit from extremely stable ownership that doesn't really interfere with (hockey) decisions, and solid management. Jacobs is highly involved at the governors level and with Bettman, but he empowers his management team and stays out of the areas where he has experts on staff to handle the minutiae.
They long ago established an identity and have brought in player/coaching/management talent to fit that identity. Most teams don't have that kind of stability. They bounce from one idea to another, one vision to another. The Bruins don't do that.
It's not about one or two sterling players at the bottom of the pyramid (many of whom are gone now). Good organizations really are about top-down success. People often don't like to hear that (it gets dangerously close to saying that people like CEOs are properly compensated, which people despise hearing), but it's true. Your most important elements are at the top. When looking for the source of success/dysfunction, look there first.