For example, admission to most top grad schools in biomedical sciences is only possible without quota if you have publications. Guess who gets published in their undergrad more often than others? Children of professors.
In the end the reality is pretty much everyone of socio-economic privilege gets one boost or another that's not available to other groups of people. That's why I don't get mad if some underprivileged classes get "unfair" quotas as alleged by the US supreme court. I didn't get mad that rich kids can get into Harvard without too much work, why would I get mad that an underprivileged kids can do that now?