most everything is electronic now so it is very easy to look at all of the applicants from a given UG institution as a group. I can name at least 10 schools that send 30 or more applications to the med school where I'm on the adcom and most of the time I deal with applications from just one region of the country (so that we are more familiar with a smaller number of schools).
Comparing 10 students from the same school removes one variable from the mix. It also streamlines the reading of LORs because the reviewer gets to know how that school ranks students, the formulaic phrases in the committee LOR, the common extracurricular activities.
You are competing against the other applicants from your school and all the other schools, too. Your chances of getting an interview may be as low as one in 10.
To know if a lot or a few students matriculate, it really helps to have the denominator. What proportion of the applicants from x college are interviewed, accepted, and matriculate? If all you see in the numerator you really can't comment on "a lot" versus "very few".
I could fill all my interview slots with good applicants from just 10 schools. Instead, we do try to choose the best from a wide variety of schools including private research intensive universities, public universities, and liberal arts colleges.