Well besides the obvious reason that the majority of colleges just cant afford a spring floor, I like to say that its "college cheerleading." Since there is no real pro cheerleading, college cheer is what the youth strive to become one day, besides Team USA.
In a small comparison, when you look at pro sports and college sports you see the small differences. For example, the NBA shot clock vs the college shot. In college its 35 seconds, where as in the NBA is slightly more difficult at 24 seconds. Same with the three point line, where its pushed back a couple feet in the NBA.
Its pretty much like that in all major level changes, just making things harder, no spring floor (besides the money) is just one of the new challenges.