Because it is not generally recognized that the majority of the processes that are taught to biology students as "evolutionary processes" in themselves do not facilitate evolution at all but in fact work against it. People do have the erroneous idea that somehow natural selection, genetic drift, migration and other "evolutionary processes" could lead to evolution, and the fact is that they do not, they work against the possibility of evolution.
Sort of. Dawkins put it this way:
"...strong 'selection pressure', we could be forgiven for thinking, might be expected to lead to rapid evolution. Instead, what we find is that natural selection exerts a braking effect on evolution. The baseline rate of evolution, in the absence of natural selection, is the maximum possible rate. That is synonymous with the mutation rate."
Note, however, that he is talking about the
rate of evolution. What we find most interesting about evolution is not
how fast it goes, but
where it goes.
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