It's also devilishly hard to accurately research. To isolate the effects of hypnosis from the desire of the subject to please the researcher you need to administer a placebo hypnosis. However, this is very difficult as hypnosis by it's very nature creates an immediate experiential effect on the patient that you somehow must replicate in the placebo (so the subjects can't just guess whether they got real hypnosis) without actually performing hypnosis.

Also there really aren't any good precise questions to ask about hypnosis. Does it help people quit smoking. Yes, but so does placebo. Does it help people deal with pain. Yes, but again so does placebo. Before you start damning people for not investigating hypnosis describe what precisely you want them to figure out.