I see where you're coming from, but it would also be an extreme liability. For example, imagine companies demanding that you sign in with only your uniquely-identifiable government email address so they can better track you. The necessary technical qualities to resist such attacks (eg allowing any user to generate a bunch of additional nyms) will never be considered in make-everything-legible government thinking. Social security numbers and drivers license numbers are already abused by surveillance companies, and so the last thing we need is another government-issued identifier without something like a US GDPR to prevent its abuse.

Also, the kind of long term stable online identity you're desiring can already be had by registering your own domain name.