A couple of things I notice from the MA list:
Schools with higher default rates tend to be those where I would guess lower income students are attending. So of the UMass schools, I would guess the richest kids go to Amherst, then Lowell, then Boston, then Dartmouth.
The predominant majors offered at each school seem somewhat correlated with default rates. Lowell has the tech/engineering majors. Maritime is somewhere between a military academy and a vocational school from what I understand. Many of those with higher defaults have a lots of very generic degrees (psychology, general business) or education degrees.
For tiers of “directional” state universities I can say I know a lot more people who attend or aspire to attend Westfield, Bridgewater, & Worcester State than Framingham, Salem, and Fitchburg. I also think the first set might be bigger schools with more majors than the second set. So I feel like there is some self section of student quality there. If your finances dictate you go in state and you need to live at home, a better student would usually choose Worcester over Framingham, for instance.