Again, OP claimed that top US schools directly ask your income in applications, implying this information was used directly in admissions decisions. It is not, and any admissions tests Oxbridge uses certainly have similar issues of correlation with wealth.
They claim to be "need blind", but they still ask. I'm not sure when they started that policy, but a quick search claims they are only one of 5 schools that claim to be "need blind".
That is need blind for internationals, which is quite rare. Need blind for domestic students is a long list which you can see here, and includes basically every school that one would call "top": https://en.m.wikipedia.org/wiki/Need-blind_admission
They ask for the information at the same time as the application so that aid packages can be offered in a timely fashion. It can take months to process everything, and students need to know the cost far enough before the decision deadline to weigh their options.
The financial aid office operates entirely separately from the admissions office at MIT, and I'm sure this is the case at other schools that claim to be need blind. Need blind has a clear definition, and there are legal implications to being a need blind school (for domestic students) in the US. It isn't just some marketing thing.
To your point about indirect economic discrimination, I'll note MIT is very clearly the best Ivy+ at admitting low income students: https://www.nytimes.com/interactive/projects/college-mobilit...
That doesn't mean there isn't still a long way to go, but MIT is for sure not using need information in their admissions decisions, and if anything actively tries to not just take a ton of elite private school kids.
Actually, the next step probably will be to stop need blind admissions so that parental income can more explicitly be used to correct for disparity in opportunity.
