It is not uncommon for unhoused people to lose all their possessions, so even if purchasing multiple hardware security keys wasn't a huge financial hurdle, the recovery model I use (Yubikey on my keychain, two in my safe, mail one to my parents) falls apart for those on the margins of society. If email is an essential service in modern society, recovering access to it from some first principle of identity is essential. I don't have an easy answer for how to do that, but I also don't have a trillion dollar market cap.