How come bad plots make it into the anime sometimes? Don't they have QC?
Or are they fooled by "maybe-maybe" frauds?
This is the wrong SZS subject for what you're trying to talk about.
I'd go with the one on following the original work.
How come bad plots are made into movies & TV shows all over the world?
TV shows are far cheaper - it's very likely don't even have the QC, and they don't rely on DVD sales.