Most low-income and even middle-income students cannot meet the academic and experiential benchmarks that elite schools set.
I think it is interesting that high ranking schools set up very high standards, it is almost like they do not want certain students entering their institution. I have also become aware that low income schools are not supported in the same way as all these other fancy private academies. Low income neighborhoods tend to have poor funding, not as many resources, etc. Thus creating a gap in how well students can be supported and educated.