The dirty secret is that they haven't really had those supposed educational advantages for a long time, if ever.
I attended undergrad at a large university that was (and still is) around the 75-100 range in US News rankings. I then attended graduate school at a top-10 US News school. My expectation coming in was that compared to my peers in undergrad, the undergrad students I was teaching as grad student would on average be smarter and work harder, and would have better resources available to them. All three were false. They were on average more ambitious and more demanding (in terms of e.g. asking for points back on assignments), but not smarter.
There are very real advantages to attending an elite school, but they are primarily social rather than educational. Having letters of recommendation from top scholars helps you get into grad school. Making friends with other people attending an elite school can provide all sorts of opportunities down the road. Just having the name on your resume will open doors for you. The undergrad education itself, though, probably isn't better.
Not only are the students of less quality, the pace has to match the bottom, so they don't fail out all the special entries.
All those schools have going for them these days is a reputation that’s no longer deserved, social connections, wealth and a sense of entitlement that scores them freebies from time to time.
Why are people so willing to accept that from childhood leagues to professional, in basketball, football, soccer, etc. society scours and finds all the best players, and nobody is out to prove that it's not true, but that somehow we as a society are incapable doing it in intellectual fields? Does that mean that no player who didn't make it as a pro wasn't close, or that every pro player works out? No, but within the stochastic variance, sure.
Based on my own experience at an elite school (as a graduate student, teaching undergrads), this is definitely false.
> Why are people so willing to accept that from childhood leagues to professional, in basketball, football, soccer, etc. society scours and finds all the best players, and nobody is out to prove that it's not true, but that somehow we as a society are incapable doing it in intellectual fields?
Because athletic performance can be objectively and reasonably easily measured along many (not all) dimensions. Intellectual performance is (1) much harder to measure objectively and (2) much less socially acceptable to use such measurements. Good grades can indicate high intellectual performance, or they can indicate grade inflation. A high SAT score can indicate high intellectual ability, or it can indicate that your parents paid $4000 for SAT prep courses and 1-on-1 tutoring. Basing college acceptance on a battery of psychological tests might be somewhat better than current methods at selecting elite students, but (1) those tests would immediately become the subjects of a new test-prep industry and (2) it's not socially acceptable to do that.