When logging in with NIP-46, it seems much simpler for the client to generate a connection token and pass it to the bunker, especially since the signer usually has a QR code reader.
The opposite approach lacks a convenient way to transfer the token. Manual input is impractical, and copy-ppasting is impossible if the devices are different. Since you're not logged in, direct messages aren't an option either.
I was curious why so many Nostr clients only support the latter method, but I recently realized while making modifications at jumble that nostr-tools only supports it.