In addition to all the excellent reasons given there is another MAJOR reason. It's because there are 80 pages of lawyers in the phone book ready to sue the socks off the doctor if anything at all were to go wrong. Doctors have to go by what they call "standard procedure." If they deviate from what every other doctor would do in the same circumstance they risk being sued.
Doctors are about useless unless you've just been run over by a hay baler.