I think that it really does depend on the therapists theoretical orientation and also on practical constraints.

Therapists who work in a public service usually have guidelines that they are expected to follow. People in private practice typically have a bit more leisure to do as they please.

Different therapists feel comfortable treating different things. Some believe that once per fortnight is optimal for the kind of work they do and so they wouldn't increase that whether they could or not. Others believe that once per week is optimal. Others believe that twice per week is optimal. My t said he thinks this would be optimal for me but he doesn't have the available slot... Others believe that three times per week is optimal. Sometimes they vary it depending on the kind of work they are doing as well. Or for different clients with different issues (e.g., more sessions for clients who have trouble feeling attached or for trauma work).