a and c can be solved by making it an option for 2fa instead of requiring it.
but you already know what will happen next, don't you? People would stop using 2FA, then some donkey on government contract with access to nuclear weapons gets hacked, and everybody would lose their mind: "how could google be so stupid to allow people not use 2FA?!?!?!"
I'd be asking why was someone using gmail for anything related to nuclear weapons.
I don't know if you are being sarcastic or naive here... Why would Hillary use her own email server for critical government correspondence? I don't know! Reasons I guess. People on all levels tend do stupid stuff every once in a while
a) google will have to require a credit card in order to open an email
b) person opening an email account must actually have a line of credit, e.g.: many of the people mentioned in the OP will not have it
c) opens a new attack vector on google accounts, e.g.: people who secured their emails using 2FA app for example can now be attacked via a credit card process