It isn't "always", but schools
that get federal money do have to prove diversity in their programs. So some few will be chosen on other than academics. We did this exercise in one of my MSN Ed classes; given a pool of "applicants", with race, GPA, gender, experiences; and told to choose 20 of 50 "students". There were five groups of us that did it, and not one of our lists came up even vaguely the same. Each group weighted things differently (by accident, not instructions
My school has a points system, goes by TEAS, GPA, and 1 point for being instate. No other consideration made, so no race/gender/age preferences make it into the decision. Unfortunately, we sometimes get people who shouldn't really be there, but don't find that out until they've been in the program a while; usually they withdraw on their own.