If nothing else, the idea of having a separate e-mail account/inbox per use case is an interesting one!
Much like those people that use aliases or something of the sort to be able to tell where who sent then a particular email, like if suddenly some [email protected] started getting random marketing mails.
> If anybody, it's the sites having the problem of missing users.
I mean, isn't that just the consequence of websites optimizing for whatever seems to work for them and forgetting about the minority of users? It might be missed profit, sure, but that depends on just what portion of the users view this as a dealbreaker.
Maybe there could be an app like Google Authenticator that would offer login to multiple websites through one's phone? We already have that in Latvia somewhat, for banking - you enter your user details in the web form and get a prompt on your phone for your PIN to log in with in the web app: https://www.smart-id.com/