The admit rate by score page of MIT’s website links to the following quote that explains the difference between correlation and causation well:
Now, I and others are on the record as saying that we admit people, not test scores, and that in any case there is really not a difference in our process between someone who scores, say, a 740 on the SAT math, and someone who scores an 800 on the SAT math. So why, as the commentor asks, is there such a difference in the admit rate? Aha! Clearly we DO prefer higher SAT scores!
Well no, we don’t. What we prefer are things which may coincide with higher SAT scores. For example, a student who receives a gold medal at the IMO is probably more likely to score an 800 on the math SAT than a 740. But if we take an IMO medalist (with an 800) over random applicant X (with a 740), does that mean we preferred an 800 to a 740? No. It means we preferred the IMO medalist, who also happened to get an 800!
It’s a similar idea with perfect stats in general. There is a far higher admit rate for perfect stats than the average, but that does not mean the perfect stats are the primary driver of that higher admit rate, and the colleges are obsessing with the difference between an imperfect 790 SAT vs perfect 800 SAT. Kids who have perfect stats are probably far more likely than the average applicant to have national-international level ECs/awards, stellar LORs that talk about best in years, incredible essays, certain powerful hooks, etc. If you have an applicant who just has perfect stats and not the amazing non-stat factors, then I’d expect the admit rate to be quite low.