Why not have key export and import?

Are they my keys or not?

>> Just create new passkeys on whatever device or service you want, and register those as well.

I would rather not have different keys for each device for each account. It is an unnecessary combinatorial explosion of keys that requires more effort than is really needed.

When you get a new device, you need to generate and add new keys for every account. Why can't you just import existing keys?