It’s my understanding that what is described as “T14” includes all schools ever ranked in the USNWR top 10. Depending on year to year rankings, that’s a number that can always grow.
And it seems to me also that law schools would give credit for the relative nature of difficulty of a major and the relative reputation of a college. However, I’d note that the law schools mentioned as T14 also seem to take pride in the number of different undergraduate colleges from which applicants were admitted.
So I’d say that a bunch of factors are in play, including astonishing GPA/LSAT numbers and interesting life experiences(broadly defined-Yale notes it accepted an eggplant enthusiast; your guess is as good as mine as to what that means).
I’ll stick with the idea that really impressive people get accepted at the top schools.