They fear it, because purpose points to a super-intelligent Creator. Therefore, evolutionary theory requires total randomness in everything made. Yet all about us we see purpose in everything. The animal is given legs, eyes, ears, and marvelous internal organs. Everything is purposive.
Nothing is random or haphazard.
Staying by the average. Statisticians well-know that all living creatures tend to keep coming back to the average. Even though varieties can be bred, if not continually guarded, their descendants will tend back toward the average. The offspring of the gifted will move back toward the mean, or mathematical average. Mutations are the only way that something quite different from the average could be produced.