comment: >
  
  Simply because of the paper work and beaurocracy required to perform a clinical trial. Therefore the cosmetic industry run "volunteer studies". They still require ethics etc. but you can set up your own ethics committee and pass off your own experimental protocols.
context: Many years ago a girl I knew volunteered for testing instead of animals. She lost all of her eyelashes when testing a mascara. >
  
  Ugh, why would that be a volunteer thing? At least clinical trials almost always compensate you with cash.