In theory, at one point people will be done with therapy. I think a better analogy is a physical therapist; you go to one because of an injury.

A personal trainer is for boosting your physical health / performance. For mental health, you'd get a coach, training, or read one of many self-help books, not a therapist.

There are multiple kinds of psychological counseling. Some "supportive therapy" really is more of an ongoing thing, like having a personal trainer. Some kinds of psychological therapy always aim to have a terminus, like physical therapy.