I can't think of many things more likely to induce a horrible trip than some credentialed "therapist" telling me what to do in a "clinal setting".
The point is that the exact people who are well-known and respected as black-market guides would become therapists in a world where such a profession were legal!
Not entirely true, although only a few, there have been and continue to be legal studies involving psilocybin (also MDMA) in addition to the one in the OP.
Here is a smoking cessation study in Baltimore, involving a psilocybin psychedelic trip. https://www.quitsmokingbaltimore.org/
Here's an article about the findings of the 2014 pilot study on the same thing which describes the methodology to some extent. https://hub.jhu.edu/2014/09/11/magic-mushrooms-smoking/
But specifically in this context psychedelics are generally introduced to individuals who haven't had prior experience with them, and may need additional support that therapists can help with (e.g. survivors of sexual assault, deep depression, anxiety regarding terminal diagnosis, PTSD, etc) and the therapist have been trained specifically in guiding these individuals in psychedelic trips. So they are like the best trip sitters you can have if you are trying to get out of rut.