Because the process is stupid. The NCAA can't just let high school football players enroll at a school. They have to have this two-year, convoluted process involving summer camps, verbal commitments, unofficial visits, official visits, offer letters, quiet periods, dead periods, letters, emails, phone calls, texts, in-home visits, in-school visits, letters of intent, fax machines, scholarship limits, counters, walk-ons, blah blah blah.
Eliminate any of it and what happens? Nothing. Say 100 kids enroll at Alabama. A full 80 of them would transfer the first semester because they'd never see the field. How is that any different than now?
The current process is a bureaucratic nightmare.