It’s that they’ll receive MANY more applications from fully qualified students than they can accommodate.
There are nearly 28,000 high schools in the US. That means there will be at a minimum, that many Valedictorians and that many Salutatorians looking for slots at schools. At a minimum…56,000 graduates ranked #1 or #2 in their class.
It’s not about qualifications. It’s about too many students applying to too few schools.