Why Can't Decrypt with Public Key?

What you need to do is read up on Public-Key Cryptography. The short answer is it is based on an algorithm that allows one key to encrypt and the other key to do the decryption, which is why you cannot work backwards.

Can you use public key to decrypt?

Data encrypted with the public key can only be decrypted with the private key, and data encrypted with the private key can only be decrypted with the public key. Public key encryption is also known as asymmetric encryption. It is widely used, especially for TLS/SSL, which makes HTTPS possible.

Can you decrypt RSA with public key?

You don't need to publish the private key at all - RSA is a trapdoor permutation which means: If you encrypt with a public key, you can decrypt with the private key. If you encrypt with a private key, you can decrypt with a public key.