"So if we're talking these types of theories, let's say we have a good mix of: Implementation of non-euclidean geometry into real life engineering, very advanced quantum tunneling, government experiences "gone wrong", hallucinations, a lot of construction materials and slaves to build everything. If we're "realistically" talking, of course."
Then there's The Lost which is really ancient, decimating that theory.
Besides, if the Backrooms itself is man-made, how the actual fuck is it outside the fucking universe? How the fuck do people like ΩMEGA exist?