I think that’s a pretty closed off view of self help. Especially since earlier generations, particularly men, were sold the whole “men don’t cry” and “put up or shut up”. Essentially gaslit entire generations believing that forcing down emotions and emotional introspection out of their lives was the right thing to do. So it filled a market gap. Especially ones written by professionals, specifically in mental health or philosophy.

I’ve also seen (and personally received) testimonials on their effects. Shit people have literally read their way out of a smoking addiction (Alan Carr for my dart munching friends). That’s not to say there isn’t a lot of trash out there cashing in. Just the “everyone knows they don’t work” line irked me into replying.

have been for like, 30 years now?

The genre is much older than this. The market is huge (something like 10-15 billion $USD) with about 50k different self help titles being published every year. Obviously no bookstore is going to stock 50k different self help titles (except maybe Amazon). But much of this market is served by special interest bookstores, like religious bookstores attached to churches or whatever. And those have existed forever!

I'm old enough to remember the 1980s and the parenting advice books that told my parents to beat me with a wooden spoon -- that they purchased from their church. It biases me against the genre somewhat ;)

Self help books tend to be part of a radicalization pipeline, where the authors are considered "experts" because they have a published book. Once you're in the pipeline, like youtube conspiracy videos, eventually you'll end up buying into antivaxx and other woo.