[aheieosnssisowi]

You can't see a good reason to validate form inputs client side and use the exact same validations server side?

[pphysch]

That's nonsense. There are many validations that you don't trust to client to handle (or will require API calls, making "exact same" an unreasonable expectation). Ultimately, frontend validation is for UX and backend validation is for security.

Different concerns, different capabilities, different code.