I too think it's a mix of ignorance, prejudice, wanting to feel that we are in the therapy that is right for us (maybe a fear that it isn't, or just a speck of uncertainty or insecurity about that), and a real concern for others and a (guided or misguided) desire to help.

I was (and probably still am, but not as much) prejudiced against some forms of therapy. That comes from my personal experiences. Some therapies weren't helpful to me at that time so I concluded that it was the therapy (not ME! lol).

There are so many kinds of therapies (and therapists) (and patients/clients). Ignorance or unfamiliarity is a given. I have learned so much by reading. I may not be able to understand or appreciate another's therapy in general, but may find some aspects of it I can relate to.
I also have learned to distance myself from the site sometimes when I feel like my own therapy is being affected because I start wanting my therapy to be just like someone else's therapy. I can start to become dissatisfied with my own therapy, when I am in fact very happy with my therapy.