Another item that has not been mentioned here is that the elite colleges seem will change their admissions standards in order to prioritize yield. In some cases, this means picking kids because they are less likely to be accepted at or want to go to your immediate competitors.
There was an academic article some time ago that analyzed Princeton’s admissions with Harvard’s, and noted that after a certain point, the acceptance ratio at Princeton declined with increased test scores. The explanation was that the tippy top test scores (36 ACT) had exhibited a strong preference for Harvard over Princeton in the past, so Princeton was less likely to accept those tippy top test scorers in the future unless there were other factors that indicated they would prefer Princeton.
Tufts syndrome is an extreme version of this phenomenon, but every school wants to be able to discern who will come if they are offered. Early Decision is the easiest method of doing this, and is most heavily practiced at schools that want to maintain low acceptance rates and high yield rates but lack the appeal of the top 5. Outside of ED, schools like Vanderbilt and WashU prioritize test scores because they know that HYPSM do not. There will be a certain subset of 4.0/36 ACT kids who write terrible applications and get denied at the top 5 schools, and these kids are more than welcomed at the lower schools.