That's a great question, I'd bet it's fair to say that 80% of their applicants would not qualify, and yet it opens the door for some really deserving humans.
(Not being able to afford it is why I didn't go to MIT, I also wasn't accepted at Cal, yet UCLA (and all of the UC system for that matter) was under 4,000 a year and that's what my folks and I could afford so that's where I studied.)