Usernames have always been easily lost
Going back to the dark ages of email on the Internet when your email was always issued by either your employer or your service provider - even then you could have several email accounts. Lost password? no problem - there was always an IT person who could either give you a new password or reset the account.
Then Netscape and Apple got into the game and started giving away email accounts. BUT - there was no retrieval process for email passwords, so if you forgot a password you simply created a new account.
Now we are several generations down the road and folks like Google and Facebook are attempting to actually link the identity of an account to a real person - easier said than done. A government provider would have to issue email addresses like drivers licenses or passports with an absolute 1:1 correspondence where all aliases are linked to the master record. Even then there would probably be a black market in fake addresses.
As for bots using email addresses - that will continue until all emails are absolutely verifiable back to a real person. For various reasons, many governments are reluctant to embrace this - Think privacy for the EU and skullduggery for Russia. Other governments love the idea - like China - because it makes internal security more straightforward.
Rule of thumb: divide all the hype about numbers of people reached by 2 or more.