It's not about the colleges, it's about the high schools. Some of it's an effort thing for students, some of it's a culture thing ("I'm bad at math" etc).
A lot of it, though, is that American public schools serving poor communities usually suck. So poor kids get to college and are told to do Calc when they haven't been taught to do basic algebra, whereas the rich kids had good teachers, the chance to take AP classes, etc. Since many minorities statistically are poorer on average, this translates to ethnic differences in performance in college.
The colleges are trying to do what they can to address the problem, but there's only so much they can do with the demographics of applicants they're given, especially a community college that's built to be cheap and available to anyone.
