It seems like the most common schedule for therapy is one hour (50 minutes) once a week. Why is that?

Are there studies that have shown that is the most effective length of time for a psychotherapy session? And that once a week gives optimal results? Or is it just historical? When people are studying to be therapists, do they tell them to stick to this plan? Is it due to what insurance will reimburse for (not the issue for my T, since insurance does not reimburse for his services)? Is it to keep therapists from taking financial advantage of their vulnerable clients?

It seems like so many of us here angst about increasing our therapy time each week. I would love to see my T twice a week. I have so much territory to cover and I want to make really fast progress. Only 50 minutes a week slows me down. Each session I have a huge amount of stuff I would like to fit in, and it is impossible. Two hours once a week would be great. Or one hour sessions twice a week would be good too. I could make so much progress. Why is that not acceptable if one is willing to pay? Have studies shown you need a full week between sessions to process what was discussed? Or that T needs a full week between the same client to recover from him/her, lol?

Other professions that have clients are not like this. I saw my lawyer yesterday for 3 hours straight. It was a great session. I had a long list of questions and we just kept talking until I had all my answers. Why is that so bad? It made me long for that with my T.