Why is GPG agent forwarding not enough to get SSH keys working on the remote?

[mainrs]

Maybe I am misunderstanding something. My understanding is that GPG agent forward would be enough to get both dec/enc/sig functionality working on the remote machine.

Since the SSH key is derived from the GPG key, I don't see why the remote machine has no access to the SSH keys. Even importing them manually on the remote using gpg --export-ssh-key $KEYID does not work. I get an error trying to load the key that says Load key <path>: error in libcrypto. I don't really understand why to be honest.

Thanks for helping me!