It's not "hard" for regular users; it's a complete non-starter for regular users. Every "non-custodial" or "self-sovereign" system of trusted identities founders on this issue: account recovery is the hardest problem in identity, and if you don't have a solution for it, your system is going to be a niche at best.
People have been coming up with these schemes for decades, and for that entire time, the near-universal de facto standard trusted identity system has been "Google accounts". People knew at the beginning that they were delegating trust to Google; they know it now as well; they are not going to adopt "names resolve to a key, the same key, in every application", no matter how many different names that scheme is given.
Yes, the UI/UX of decentralized systems is so difficult for users that it creates demand for centralized systems to manage it for them, Coinbase, Gmail, Github, Twitter, The Pirate Bay.
there's nothing wrong with a keychain or password manager holding your keys. passkeys already work exactly this way, completely transparent to the user. it's fine for most users.
People have been coming up with these schemes for decades, and for that entire time, the near-universal de facto standard trusted identity system has been "Google accounts". People knew at the beginning that they were delegating trust to Google; they know it now as well; they are not going to adopt "names resolve to a key, the same key, in every application", no matter how many different names that scheme is given.