As they mention, financial aid is the big factor. I suspect that the majority of people turning down these schools would not be eligible for significant financial aid awards.

MIT without financial aid: $67,342

MIT with "average" financial aid: $18,025

UMass in-state: $29,876

https://web.mit.edu/facts/tuition.html

https://www.umass.edu/umfa/undergraduates/costs