As somebody who studies psychology.. If a psychological study says A, it’s more likely to be actually B. The quality of research is much, much worse than people think.
"Just saying" the above is not what CBT is, though. I've had a lot of CBT and other kinds of therapy, and I've never had a therapist just tell me "so don't do that", or "do more x".
It's about analysing your own thinking(cognitive) and actions/habits(behavioral) in cases where those are keeping you stuck in a miserable situation, and identifying what you can do to change them.
Sure, if you put the most inanely over-abstracted construction on it like "just live healthier and you'll feel better", it sounds meaningless, but the implicit assumption there is that's something you can just decide to do, and succeed in. That's not the case for many people, and those people can benefit from CBT.
Again, of course, if you are a well adjusted adult, and no one in you life is clamoring for you to get therapy, then chances are, either you've pushed anyone and everyone away that cares for you that deeply, or you don't need it, both of which are totally possible.
As for if it's a scam? That word gets thrown around too easily these days. Do they cost a lot? Yes. Are you worth it? Also yes. That's not to say all therapist are equal, and someone that's great for you might be terrible for the next person, and some of them are just bad. (There are also those that are quite good!) As there are with all things. Going into therapy with specific goals on things you want to work on (eg irrational anger at some specific thing that's ruining your life) tends to help it not be just an ongoing extra expense like a gym membership, if that's not what you want. At the end of the day, they're stuck in the system as much as you are, and paying them also makes it feel more balanced in that they're being paid listen to you go on and on and help you with your ish. You wouldn't/shouldn't treat your friends so one-sidedly. That said, it's entirely possible to pay to see a therapist and not get anything out of it. I will admit to that as a possible failure mode, but it's a failure mode and there are certainly success stories out there of people turning their life around and becoming happy well-adjusted adults.
Because that part is wrong, apart from the underlying inner working being dissected in labs (the cognitive science part), the therapy part it is well studied in the wild - and it works.
> and the results of therapy I come across always seem extremely underwhelming.
So you mean anecdotes? Of course you recognize the underwhelming results - the people where it worked well are less noticable, by definition.
> Maybe for some cases like severe phobias there is something to be solved, but do we really need to be paying thousands of dollars a year
That you have to pay money has been a decision of the society you reside in. It doesn't have to be this way, and in fact it isn't in most industrialized countries.
> for a therapist to say "hey, maybe if you'd invest more in hobbies, social relationships and a healthy lifestyle you would feel better"?
That is a strawman, not CBT.
So somewhere there is evidently a lot of knowledge about effective, working psychology, even if that knowledge is used for evil rather than good...
And peoples lives can also vary in quality. If you're raised in a nest of narcissists it is likely you'll have a very skewed view on relationships and your idea of normal could be considerably different from the average and have negative effects on your social relationships. Sometimes you just need a 3rd party to tell you that's not normal.
Coming from a family of narcissists myself they quite adamantly stuck to the idea that therapy was a total scam. Though my observing their behaviors it is my believe they are really saying "Therapy is a total scam because they didn't tell me what I wanted to hear".
Most of the social "science" are a scam, but since it gives peoples some "work" it keeps going. In reality it's only value extraction and they are basically parasites of the common people but since the people in that field have a lot of power ("educated", often female, etc) it keeps going. It's like the HR department; you would rather not have them but since there are laws around it you pay the racket and move on, not other way.