The logic is something like this:
Guru A analyzes a certain number of successful screenplays and discovers Paradigm X (number of acts; sequence of plot points; common events, arcs, character types, etc.). At this stage, Guru A is being descriptive (“Such and such are the elements of these filmed screenplays”).
Then Guru A leaps from the descriptive to the prescriptive (this is what sells books, after all): “All future scripts must conform to Paradigm X if they are to succeed.” Guru A conveniently ignores successful screenplays that don’t conform to Paradigm X, or dismisses them as outliers, or tells would-be writers not to break the rules until they have first learned them. Guru A also ignores conflicting paradigms by other Gurus. THERE IS ONLY ONE TRUE WAY! Guru A then publishes these insights in a book (or seminar or podcast or online course…).
Guru A convinces Successful Screenwriter B to contribute a phrase for the book cover, something like “If only I had read this book when I started out” (which only shows that Screenwriter B miraculously managed to succeed without reading Guru A’s book).
Beginning Screenwriter C reads the book cover and thinks “Aha! I’ve found the key that unlocks the door to success.” Screenwriter C notices that not only has the book been endorsed by numerous Successful Screenwriters who read the book only after they learned the craft, but the book is a bestseller on Amazon. Beginning Screenwriter C doesn’t stop to think that while the Book has sold 10,000 copies, there are not 10,000 or more successful screenplays in the pipeline.
I don’t personally know any development executives, but it seems that the Prescription for Paradigm X has made it into the receiving end of the food chain, so that readers are sometimes instructed to pass over any submission that doesn’t follow the basics of Paradigm X. Eventually the Prescription becomes a self-fulfilling prophecy, which reinforces its sacred status as THE ONE TRUE WAY.