A motivated student can already graduate an American University in three years.
There is more to the college experience than how fast you can get through it and get to work. Teams, clubs, fraternities student government, learning to live on your own and some extra time to recover from a screw up or two are built into the system.
Lots more people want to come to college in the U.S. - our good colleges are doing fine.
We've got a lot of crappy colleges but that's another thread.
A lot of young people would rather acquire the knowledge and skill necessary to a productive career than to waste precious time in an extended adolescence. Teams, clubs fraternities, and student government are forms of recreation, and unless the student is footing the bill for his education, housing, and all expenses, he is not learning to live on his own. He is still a subsidized child.
Mostly state-run universities. Wanna get a real education? Go to a junior college or a tech college and get an associate's degree.