Seriously though, I wonder why nobody really attempted to dethrone PDF yet. How hard can it be (famous last words) to design a document format that allows what people generally expect from a PDF, but without the multimedia and interactive parts that are dangerous?
Because the dangerous parts are not the multimedia and interactive parts. These parts are rarely used. Even if you remove these parts from your PDF reader it’s not a meaningful security improvement. Almost all exploits are in the boring 2D text/graphics/images parts.
Network effect. Most documents are PDF. You would need at least backward compatibility, which would mean opening doors to the existing problem.