For some material reason, the big chunk of franchises - especially Star Wars, and the one I meatride the most Halo - took a downward spiral in quality starting in the 2010s?
My personal theory is because of the undemocratic nature of big media studios allowing and even encouraging substandard writers to steer them in dangerous directions causing hundreds of hours of talent being wasted.
The “stage” theory of economic systems, which usually breaks them down into early, middle, and late periods does seem to provide an explanation for why nearly all artistic mediums have gone to shit in late stage capitalism. Carrying capacity is reached, there are no new markets to expand into, risk and innovation is increasingly unprofitable, and the only thing that can get made is remakes and attention-span-destroying/drug-like content.