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.

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.