So, they were let go, and a new generation of young, unseasoned writers has been doing the writing.
But unlike previous generations though (heh), many of them are not even slightly interested in learning from the previous (seasoned) writers, whom they view as inferior for some reason.
Thus, the extremely low quality (idiot level) of writing in recent years.
No idea how accurate that is, but it seems like a reasonable take at first glance.
Mind you, I don't really watch US origin tv/movies any more myself due to their crappiness. :)