Because they are not applying a consistent selection pressure over the past
100 years. A few experiments place one set of selection pressures on the
bug for a few years and then the authors write a paper and go on to another
problem. For a scientist to spend a lifetime on a long term, multi-human
generation generation experiment as would be required to fundamentally
alter the fly, would mean that the guy never published an article. Few want
to do that. Even the space experiments sent up on satellites or martian
probes, which may take 20 years of a researcher's time, create complaints
that there is too much of one's life spent on one experiment. Nobody wants
to do an experiment whose results will not be published for another 10,000
years!
glenn
Adam, Apes and Anthropology
Foundation, Fall and Flood
& lots of creation/evolution information
http://www.isource.net/~grmorton/dmd.htm