Here's just my take on the whole thing. While I do think some families benefit from family therapy if they choose to seek it out, I think there has become a stigma in society today.
When my son was diagnosed with Autism, I had the most ridiculous hard time finding a therapist who would work with him. 1) most therapists do not work with children in my area. 2) most therapists aren't trained to work with Autism and sensory issues.
I spent months searching for a therapist for my son with the help of a case manager from his insurance company. We called everyone on the insurance approved list together. Out of everyone listed there, only 2 would actually take him as a patient. One said that he would need to go 3x a week during school hours. The school said no way, he needed to be in school. Then the second one would see him but was such a busy office that it was hard to get a regular appointment, and insurance wouldn't cover it. We finally found a therapist that would see my son, but it took a very long time. (One group of therapists referred us to family therapy and said they didn't recognize Autism at all.)
It's been a huge struggle but I plugged through it all and my son is much better off now. His current therapist also meets with me individually and my daughter, and at times, all of us together. She really helps us understand what my son's viewpoint is and how we can establish more structure and routine as well as how to handle crisis mode when he has meltdowns.
I think the stigma comes from two directions. 1) Families feel threatened by having other people in their business. 2) Not all therapists are right for each family. It takes a really special relationship between therapists and families to build trust and understanding. Finding that therapist is the key to successful therapy, as well as the willingness of the participants.