Because most people know nothing about writing. Heck, most people actually wanting to write know nothing about it and will never produce anything of value. People like Gohdroger or that user "Salah whatever" here lack an authorial mind, they're either literal teenagers or at least mentally didn't grow past that, so their fanfictions are overcomplicated messes that no serious writer would look at and say "Woah, this is quality". "Less is more" is a lesson that pretty much every advanced professional learns once they've grown enough into their area, and such theories are the opposite of that.
There's another user here who forces himself to write ugly to the point of exasperation that keeps posting his theory about the One Piece treasure being a cyborg heart. It's so, so, so, so out of touch from anything a real author would write, let alone Oda, it renders everything about it just pointless to read.
It's just so ridiculous.
