Simple. Corruption. It is not only rich people who can do it, it happens elsewhere as well, just with less money involved.
Here is one apparent example:
Teen denies cheating on SATs: 'I won't let anybody take my dreams away from me'
I don't know if the girl in question was cheating or not, but the local authorities certainly seemed to think that there was some sort of collusion going on at that test center.
Special skills and diversity should not be a consideration for admission, academic performance should be the sole factor. Being given the chance to attend an elite university should not be a compensation for experiencing hardship in your life. People who have experienced hardship are just as capable of doing well on these tests if they apply themselves btw, so that is not an excuse. What actually happens is that people from that sort of environment, a culture of failure, never learned how to do that in the first place, which is why for the most part they can't do it. Getting a free pass later in is not going to correct that if they have not already acquired the required skills.
It should be noted that the whole "special skills" factor was what allowed the current scam to work in the first place. If it was straight up academic credentials only, the "side door" would not have been there to be exploited.
For what it is worth, all the coddling will not help you one little bit when it comes to actually passing courses when you get to one of these universities, even if you are rich. You have to do it yourself, no one is going to help you. That is the whole point of a university and why it is completely different from a high school. Having money might help you get in, but it is not going to help you stay there.
One more thing, smart parents tend to have smart kids on average, while dumb parents tend to have dumb kids. Smart people tend to make more money than dumb people. Those two things correlate when it comes to overall academic performance from a socioeconomic perspective, which is why most of the people who attend these universities tend to come from higher income families. The argument that lack of opportunity makes it that way is not really true. If you are successful in life, chances are you will have kids who are reasonably successful as well.