Why this over just making every client a NIP-46 signer that can not only log you into other services, but also sign events?

This option seems like it would work for log in, but not for anything that actually requires signing of events.

Consider how most users onboard to Nostr. They download a client they heard about like Primal, Amethyst, or Damus, and they generate their keys in that client. So that first client is going to have their private key unless they have a friend who helped them get set up through a dedicated signer app like Amber. If that's the case, then those "flagship" clients ought to be able to serve as remote signers, similar to how Gossip on desktop can be a remote signer, allowing users to log in and to sign events from the client where they generated their keys.

NIP-97 seems to just allow the first part, which is unnecessarily limiting when we already have NIP-46. We would just need a more smooth way for a website to request a connection string from the remote signer app/Nostr client.