Because life is self governing by its own postulated decisions, and when in a condition of reduced strength it is suggestible in the extreme. Suggest to an eagle that he is a field mouse, and if he is in a mental state to take your suggestion on board, he will be very depressed.
Furthermore your assertion that the doctor in my example should not "further the illusion" indicates exactly the sort of loop and prejudicial conclusion (and desire to enforce agreements) that I am partly complaining about.
Don't get me wrong -- I am all for physical science, and am a regular reader of Science NEws, Phys.org, and other literature in the field. Doing brain scans is wonderful interesting stuff, i concur. I have seen nothing in the literature that really indicates that the phenomena is any more than a reflection of cognitive precursors. The idea of non-physical cogntive precursors, of course, is unuseable to physicists, and this premise glues them in to a "thought from brain" model (as distinguished from, say, a "thought into brain" model) as surely as Harvey's detractors were locked into the tides and humours model of circulation and preferred (in some cases) not to even think about pumps and pipes as an alternative model.