Cofounder Shovel.Company
https://notshant.xyz

Passport number/SSN/Aadhar etc are identifiers. 
govt-issued & controlled, globally unique (nationally namespaced), but not human friendly

Mobile Number is an identifier, globally unique ( geographically namespaced), issued & controlled by your telecom provider, not human friendly

Email Address is an identifier, globally unique (namespaced by provider), issued & controlled by the email provider, human friendly

Public Key is an identifier, globally unique, self-issued & controlled without requiring any 3rd party, not human-friendly

The proliferation of an identifier is driven by the use case. 
100% of humans have a name because it is used to address them. 
>90% of humans have a mobile number because it lets you connect & communicate with people.
~60% of humans have an email address

Govts try to increase the number of people having national ids by making it compulsory for usage when you have use cases that involves them like international travel, voting, ration, etc.

Similarly, compelling use cases built around public keys will result in the proliferation of public keys as a globally viable identifier. 
Ethereum/Blockchain is an example of an economic use case that got public keys to ~40 mil people

People don't use identifiers just for the sake of them, we already have too many to remember. 
Use cases that solve real problems at scale are what's needed to increase the reach of public keys

Name is an identifier that is self-issued & controlled but not globally unique (multiple people can have the same name), human-friendly, made legible by claiming it so in your birth certificate