Therapy should not be endless. It needs goals and a solid plan.
Therapy of any type needs treatment planning, which by my definition is an agreement between the therapist and client(s) as to what the goals are, the steps needed to meet those goals, and about how long that will take. It's often less than completely cut-and-dry, but that's no excuse for endless therapy. Treatment planning is expected in medicine (and from your mechanic!), and why should mental health be any different? Furthermore, therapists are fundamentally selling a service, and the customer should expect value for money, meaning an endpoint where they get what they paid for.
The way I see it, therapy is like a good story, a narrative with a beginning, middle, and end. It's interesting. It's engaging. Any mental health issue, marriage issue, or trauma issue is largely terrible because there seems to be no end in sight, and each week brings more of the same. Therapy ought to present a different picture, a plan that offers hope, even if the treatment is complex. AAMFT statistics show that for marriage therapy with an LMFT, the average number of sessions is 12. On the other hand, it is generally agreed among trauma/dissociation experts that the safe and effective treatment of Dissociative Identity Disorder ("multiple personalities"--extremely rare, and usually the result of severe torture/humiliation in early childhood) will usually take 5 years or more. The common denominator here is that there is a clear plan to reach set goals, a timetable, and the involvement of both therapist and client in planning.
Early in my career, I had a client who had seen the same therapist "off and on" for 20 years for depression. There was no real plan except to talk about her week. She felt better after seeing the therapist, but nothing changed in her life. Her hairstylist knew about me and suggested that she try something different. As it turns out, the origins of her depression were not complicated, and after seven sessions, she was no longer depressed. The difference? A plan, and the scientific method to achieve it.
Have you been in therapy for a long time? You may feel better when you go, but ask yourself--has anything changed much over time? For some, mental health is like a car: you go through the week, run out of gas, drag yourself to therapy, and fill back up with positive energy. That wouldn't be acceptable practice from a car mechanic!
However--note also that therapists cutting corners may result in less cost, but shouldn't be considered value for money any more than buying a used car that has been in a few wrecks. The therapist should be able to express clearly the scientific justification for the projected length of therapy (or any extension required). I feel that therapists are tempted to provide sub-par services by client request, to keep their schedules full and to avoid bad reviews.