Why can’t modern manufacturers make flexible nibs as good as vintage nibs

The only true answer to this question is, “I have no idea.” Of course, my not knowing the answer to a question has never stopped me from trying to answer it. But, I have written a blog post about this very topic, which you can read here: http://penhabit.com/2017/06/17/why-cant-modern-manufacturers-recreate-vintage-flex/