(1) Randi is condescending and downright nasty to people who identify as psychics. $1M might not be worth being in his presence, let alone scrutinized by him.
(2) Randi has a lot invested in being right, so the tests could be downright rigged
(3) Many psychics propose all humans radiate quasi-electromagnetic energy, and their power comes from consciously directing it. Randi could therefore be unintentionally interfering.
(4) The test could be inadequate to describe the psychic phenomenon. For example, the psychic could be skilled at generating a particularly strong placebo effect, which would get written off regardless.
(5) The results might dismissed because they would invalidate too many existing theories, all of which have been constructed on the assumption that psi does not exist. A frequently accepted circular argument.
I'm not saying any of these explanations are true, but I am saying that no one knows either way.