Still don't understand. By expanding the pool of admissible students (including those with other attributes than academic), don't they increase their rates?

This is a little beside my point, which was that competition will remain as long as schools remain selective ("selective" defined for the sake of this argument as accepting less than 100% of applicants). Even if there was a broad increase in admission rates, people would still compete to be part of the X% accepted to "top" schools.

To address your point, though, I'll assume your use of "admissible" is synonymous with "admitted" students. An increase in rates would require that the number of admitted students increase relative to the size of the applicant pool. If the applicant pool increases with the number of admitted students there isn't necessarily an increase in the rate of admission depending on the relative increase in the size of the applicant pool. If we instead define "admissible" as meeting criteria for admission but not necessarily being admitted, I wouldn't be surprised to see a corresponding increase in admission standards to maintain existing admission rates. Interested to see if anybody has evidence to support or refute this based on historical trends in admission criteria (GPA, SAT, etc.) vs. admission rates.