There's ways around it... the identity mechanism supports multiple keys so you could have a backup in escrow.
But most people don't want to worry about key management at that level. Hell, I know exactly how everything works, and key management still scares me. The consequences of a mistake are huge.
Yes, that key is screwed because it's lost, stolen, at the bottom of the river, etc. But this is when you generate a new key and store that pubkey at your PDS so the Appview can find and index your new posts from your new phone. It's the same thing that happens when I reinstall Debian on my Thinkpad and upload a new ed25519 pubkey to Github so I can push again.
There's ways around it... the identity mechanism supports multiple keys so you could have a backup in escrow.
But most people don't want to worry about key management at that level. Hell, I know exactly how everything works, and key management still scares me. The consequences of a mistake are huge.