I think people have forgotten how to write good movies

No, they still write good movies. The problem is that the money-men will not fund good movies because all they want is a big return on their investment. That means that they only fund sequels and spinoffs of previously successful properties. Only on rare occasions does anything new get funded and even then the decision is based on something other than the quality of the story.

There are lots of good stories out there that will never get turned into movies or shows simple because the people who make the decisions are trying to make money rather than art.