The NCAA won't (and hasn't) done something like that because then top HS players would be heading to Europe instead of playing in college. The NBA isn't going to change their rule (Why get rid of a free minor league with a huge publicity machine to hype future stars?), and the NCAA has no leverage against the NBA.
I would have agreed with you completely 3-4 years ago, when Oden and Durant electrified the NCAA, became huge stars, and sparked a huge debate about who should go #1. That was sort of the peak of great freshmen who went straight to the NBA and made an impact: Carmelo and Bosh several years before, and then Rose, Beasley, K-Love, Eric Gordon, and OJ Mayo the year after. Those guys were stars before college, during college, and then right away in the NBA. Look at the last couple of years, though, and it gets pretty bleak. Here's Chad Ford's mock top 10 for this year:
Kyrie Irving, Perry Jones, Jared Sullinger, Derek Williams, Enes Kanter, Harrison Barnes, Jonas Valuncunias, Jan Vesely, Terence Jones, Kemba Walker.
That's five freshmen, three Euros, and exactly zero guys that have the star power of guys like Melo, Rose, or Dwayne Wade coming out of college. Look at the last couple of drafts: there have been exactly two freshmen who have come out and actually made an impact (Wall and Tyreke Evans). If you're an NBA team, would you prefer to draft Perry Jones (who isn't going to sell a single season ticket) after his first year and teach him how to play basketball, or would you rather get two more years to watch him develop, hopefully become a star, and get ready to contribute right away?
There have been two historically bad drafts in a row and we're staring down a third. From the NBA's perspective, something's got to change, and soon.