It's a bit more nuanced than what you're describing. I suggest listening to this (or reading the transcript): https://www.nytimes.com/2024/01/17/podcasts/the-daily/the-wa...
Transcript: "So this in-depth study looking at college admissions that was released last summer ended up finding that the richest applicants have huge advantages in college admissions, and a lot of people have assumed that the SAT must be one of the advantages that richer applicants have."
Then they controlled for the obvious confounders, and the assumption was wrong. (Big surprise: Wealthy people attend better schools.)
I, too, am curious why schools changed their admissions policies before studying the matter closely.
Probably for the same reason Oregon decided to decriminalize most drugs thinking it would reduce usage and harm (it didn't).