Do you think that it's rare that the poor are the most capable? Presumably, if the poor are underrepresented at these schools, they're missing out on a lot of potential people who are very capable. I studied at Harvard and certainly wish the student body were more economically diverse, as challenging of a problem as it is to solve. It can be very hard to identify highly capable high schoolers from disadvantaged backgrounds since they often don't go through the sort of differentiation that the wealthier high schoolers coming to schools like Harvard do (top high schools, academic summer programs, research at local universities, et cetera). And that's ignoring the problem of getting them to apply and attend.
I went to Amherst, which has made a very concerted effort both to make an Amherst education affordable to low-income students (the school is free for people making under $60K/year, and has generous financial aid for the $60-100K range) and to recruit from low-income neighborhoods. I've heard it has been...challenging. It's very difficult to find students from low-income backgrounds who can handle a freshman Amherst courseload. Heck, I found it quite difficult as well, and I came from a solid middle-class background, had aced my SATs, passed 8 AP tests, etc. The school has had to bump up remedial tutoring and study-skills courses particularly to low-income students.
It's hard to catch up with 18 years of systemic advantages in one year.
Now, I do think that over a lifetime many people who grew up poor are as capable or moreso than people who grew up rich. But it takes time, effort, and opportunity, and if any one of those is missing, it doesn't happen. College may provide the opportunity to students who put in the effort, but without time...they can't catch up. Students may put in a sustained effort over a long period of time (I think this may actually be the most effective approach, as opportunities tend to come to people who do this), but without opportunities, they'll go nowhere. Or we could set up a concerted system of opportunities over a time period ranging from pre-school to college, but unless you can convince people that it's worth the effort, they won't make a difference.
Interesting how you thing it is obvious that you are more capable than low-income folks with the same test scores as you, or that you assume that there aren't low-income students with the same test scores as you.
Edit: grammar