Listing key management as the thing that makes distributed protocols hard seems like an error. If your stuff is in the cloud, what are you using to access it? Some kind of password, TOTP, etc., which is maybe tied to your email, which itself is tied to some password, TOTP, etc. So what happens if you lose access to your email or whatever they're using for password recovery? You lose all your stuff.

But it's even worse in that case, because that can also happen if they mess something up. Your email account got banned by some capricious bot, or the provider abruptly decided to stop providing the service, and then the service tied to it decided to send you a verification code to the email you don't have access to anymore -- even though you didn't forget your password for either of them. So now you have even more ways to lose all your stuff.

Meanwhile if you were willing to trust some email provider to not screw you and you only needed some way to recover your keys if your computer falls into the sea, you could just email a copy of them to yourself. And then you wouldn't be relying on that provider to have the only means of recovery, because they're still on your device too.