There are other value propositions nostr offers than owning your key. For example, a community member being able to run your infrastructure (a relay for use with flotilla). That's a more familiar selling point, and since the key storage is done in a trusted context, the small possibility of the key being leaked to the community admin can be overlooked. I'm looking at this specifically in terms of a group of people who are highly interested in one particular nostr application, and completely unaware of nostr as a whole. Even if they have to burn their key, it's an improvement because they learn what keys are, and that nostr exists.