Your experience with CBT and therapy in generally, is truly mostly determined by a good fit between you and your therapist (this isn't just my opinion, essentially all psychotherapy effectiveness research has shown this).

Also, CBT should not be about positive thinking - it is about realistic thinking. Some situations are just terrible, and a good therapist acknowledge this and validate your feelings. After you process them, they might help you think about whether there is a lesson in what happened. Sometimes people DID contribute to the situation (not always, like in the case of abuse), and a therapist might go over what you would do (even if you have 20/20 hindsight) differently.

Not all CBT is created equally - it is a theory that guides a therapist's treatment. The "quicker" CBT, which is what people seem to object you, is geared toward very concrete problems - e.g. panic attacks, OCD, insomnia, etc. It essentially gives you some skills to cope.

There are other "deeper" CBT based theories, and they tend to explore core beliefs/schemas (much harder to change). Guided by this theoretical standpoint, a therapist DOES explore the childhood origin of the schema and how it has affected you in the past. Then, they explore the assumptions you make about yourself/others/the future and how you have been "coping" based on your assumptions.

The goal is to gain insight on the fact that these maladaptive assumptions/ways of coping have contributed to some of the things that have happened to you (a good therapist does NOT place blame on the patient). A therapist then helps the patient do "experiments" to see whether these assumptions are true and helps change the way you interact with the world. They are not focused on necessarily seeing the world as a positive place, but coping with suffering better.

I think a CBT therapist does great disservice in discouraging feelings or reviewing the past. For this reason, it is important to ask a therapist at the beginning (or even during) treatment what they mean by "CBT" since not all therapy from a specific orientation is quite the same.

Other external factors also influence a therapist's approach - such as insurance, financial issues, etc. If there are time constraints, a therapist doesn't have the luxury of "going deeper" or developing the therapeutic relationship as much as they would like.