Cats are extremely visual creatures with powerful eyesight but they need to be oriented forward in order to use their amazing vision. Walking backwards would mean giving up one your cat’s most powerful senses!
Kittens are constantly learning how to move around efficiently and that can often lead to them doing silly things including walking backwards. It’s pretty common to see kitten walk backwards when they see something that surprises or startles them.
In most cases, a backwards walking cat isn’t a problem. But, if it’s happening without any explanation then there might be an underlying illness in your cat, such as Feline Cognitive Disfunction or Vestibular Disease.