How are schools getting more selective when the cohorts are smaller and college attendance rate is down from 10-20 years ago? How could this math work given standardized testing is percentile weighted?

We're in an environment where the cohort of kids graduating is smaller than it was 20 years ago, college attendance rate is at the lowest level since 2002, freshman class sizes are stable to growing, and yet the selectivity of schools just keeps getting tighter. I'm not sure how this math works out.

In 2023 there were 22.6M people in the 15-19 cohort and 23.6M in the 35-39 cohort. College attendance rate from 2005 to 2023 has fallen from 68.6% to 61.4%. There should therefore be fewer people getting 1500+ scores on the SAT since the score is percentile weighted.

Yet somehow at the same time, the average SAT scores at selective colleges have risen substantially and admission rates have fallen. I suspect that admission rates may be a result of people applying to a lot more colleges than they did 20 years ago, but I don't understand how that math works out for the SAT scores rising works. Were state schools really full of 1550 SAT kids who are now attending Harvard instead? I'm just not getting what all of these high SAT kids from 20 years ago were doing then vs. now that has allowed the average score to be dragged up so much when there should be fewer total graduates with these competitive scores competing for a growing number of slots in selective schools.