Why don't businesses concentrate more resources on finding and hiring high-quality interns?

I've applied for several internships lately, and I have my first interview today. With internships on my mind, I started considering the lack of care that most businesses put into getting high-quality interns, and I have come to the conclusion that the methods used by many businesses could use a large amount of improvement. Most of the businesses that I have applied with do not pay at all or pay a "stipend" that is below what a student can live on. Even students like myself that have only one year left of college, have very good grades, and have a significant amount of relevant experience in their field find it very difficult to find an internship that pays even minimum wage. Yet somehow, after only one more year of school, the magical degree is conferred on a person and the same person that couldn't find an unpaid internship just one year before is getting paid $20 an hour or more.

Considering all of this, would it not be much more intelligent for more businesses to recruit future employees by taking them on as interns one year early, paying them minimally, and teaching them about the business if they prove to be competent? These almost completely trained students would be grateful for minimal pay and would be prone to be quite loyal to the business that has finally given them an internship after what was likely a long search. If the student proves to be competent, they could be trained to do a specific job, hired part-time during their final year in school, and given a full-time job that they are already fully trained to do upon graduation. If they do not prove to be competent, they could be paid minimally to fetch coffee and run other errands for the summer and then let go. This situation is a win-win for businesses, which would either get a competent, loyal, new employee or a minimally paid lackey. If more businesses would be willing to put time and a little money into searching for and paying interns they would have much better, more reliable, more loyal employees in the long run. 

Image Credit: http://fistfuloftalent.com/2012/04/do-yourself-a-favor-hire-an-intern.html