
Probably because most of them come packaged with some absurd theory
behind them.  E.G. homoeopathy: like cures like.  The more you dilute
things, the more powerful they get, even if you dilute them so much
there is no ingredient but water left.  Chiropractic: all illness
stems from compressions of nerves by misaligned vertebrae.  Such
systems are so patently absurd, that any good they do is accidental
and not related to the theory.  The only exception is probably herbalism,
because scientists recognize the potent drugs that derive from plants
and are always interested in seeing if they can find new plants
that have active and useful substances.  But that isn't what 
is meant by alternative medicine, usually.  If you get into the Qi,
accupuntunce charts, etc, you are now back to silly theories that
probably have nothing to do with why accupuncture works in some cases.

Perhaps another reason they are reluctant is the Rhine experience.
Rhine was a scientist who wanted to investigate the paranormal
and his lab was filled with so much chacanery and fakery that 
people don't want to be associated with that sort of thing.  
-- 
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Gordon Banks  N3JXP      | "Skepticism is the chastity of the intellect, and
geb@cadre.dsl.pitt.edu   |  it is shameful to surrender it too soon." 