In America, the socioeconomic class of people of non-white races has been systematically kept as low as possible, through racist systems. Affirmative action (race based admissions quotas) is one tool to breach that ceiling.
In an already racist system, doing something like economic class based support (example: 20% of college admissions need to come from poor households) would just mostly go to the privileged race and perpetuate the systemic racism.
Your post is also an illustration of what white privilege can look like. I know you said you’re not American, but the tone matches to a T. White people don’t realize the negative effects of racism on others and others family history and can’t even conceive of it. From having cab drivers not willing to pick you up, to not getting a job or being passed over for promotions, let alone going to schools that are under funded. And as a side effect of that racism towards non-whites, white people benefit by getting the can, the job, the promotion, the good schools that the non-whites, but equally qualified did not.
And as the head paragraph states, that gets embedded into society in the socioeconomic trajectory of the family.