Answer by Carl Grant:
Because that is the way humans developed. Rushing into change is bad strategy. Most of our current tendencies, rules, and techniques have withstood the test of time. To have a good chance of improving things we need to proceed at a moderate rate, because change can have unforeseen problems. An example might be the attempt to cut down on forest fires. Those attempts have created larger and more destructive fires. Likewise we have been attempting to improve education for quite a while. The result has not been an outstanding success. Because of the incredible advances in technology an understanding we tend to imagine we are much smarter then our predecessors. It's a kind chronological discrimination.
Before tearing something down, you should at least know why it was built in the first place. One reason we were not selected out via natural selection was that in the past we "progressed" slowly.