Why is it always fantasy book-style magic that needs to be dispelled, rather than the sort of supernatural things that people really do believe in as adults, like crystal healing and possession by demons and magical-type conspiracy theories?

Maybe in part because when you debunk things no one above the age of 12 believes in anyway, you don't get any pushback?

Something I always found unappealing about many books of this type is how terribly safe they are. The author isn't pushing any boundaries, they're just waving the idea of boundary-pushing around and then retreating safely back into the mundane world. When I was a kid I found books like, say, A Wrinkle In Time much more engaging because they actually challenged me to imagine weird and wonderful things outside my own experience. It takes courage to write a book like that, because you're asking people to take the fantasy seriously, at least for the duration of the book, and you're taking the risk that they'll find it too silly or unbelievable. Whereas if you write a book with the message "There is actually no magic" you're not risking anything at all because everyone already knows and agrees with that.