The people who grew up in the culture permeated with such stories are stunted expressively. Because they're denied the use of an ever-growing share of the tropes and characters of the common culture. Many Disney films themselves are retellings of classic stories in the public domain. If you want to reference the original Cindarella, or Greek mythology, or Oliver Twist, you're free to do so.

You cannot do that with Luke Skywalker, or Aragorn. Now, maybe you shouldn't be able to within the author's life. But how many centuries should we keep this privilege? Would you or I (or Disney) be able to tell a new story about Hercules if copyright had been around 2000 years ago? Imagine Shakespeare still under copyright! No Hamlet or Macbeth characters in any other works without permission. We can strike several important 20th century books right there. In the future, the equivalent of Shakespeare will still be under copyright long, long after they are dead. Derivation and reuse are normal in art. Disney can borrow from the public domain to make Cindarella, but it in turn will never become public domain.