You can use a number as a unique identifier for each person that everybody stores. You can also use a number as a secret code to authenticate yourself.
But you can’t use the same number for both purposes.
Then people figured out that since the government went through the trouble of assigning every* [1] american* [2] a unique* [3] number* [4], they might as well use that as their own ID too for inter-operability between different financial firms, and that's how we ended up in this shitty situation.
Every time somebody proposes 'hey we should come up with a better national ID number' you get people yelling about mumble mumble big government mumble mumble privacy mumble mumble feds tracking you around, and the proposal dies in committee.
[1] originally only issued to those who worked, and was not exempted from the SS system, notably children. Of course these days children have SS numbers because they're a de-facto ID number, and it's required to claim dependents, and with varying degrees of resistance from weird groups like the Amish. Additionally, non-eligible people are issued tax IDs instead, which have the same format as SSNs because it was easier that way
[2] big(?) political fights over who exactly must get numbers, of course, from religious groups, illegal immigrants, and many more
[3] except of course it's not unique, there were errors where people got duplicate numbers, and people can get reassigned numbers, thereby having more than one
[4] did you know they used to assign SSNs sequentially? The guy who was next in line got your number + 1
In general, the common situations some people wish they could use biometrics--like a grocery store payment--are also ones where it won't actually be that secure. After someone goes on a shopping-spree with your stolen fingerprint, you can't really change it.
This is a fundamentally terrible idea. It assumes people must have a smartphone.
What does it take to have a smartphone? You have to commit to a monthly expense stream paid to a proprietary private company. A company who also has the power to cancel you.
No, anything that is an official government scheme must be fully implemented as a government service with zero dependencies on private companies.
True, but far too many businesses treat it as an "authentication" token that they can use to authenticate that you are who you say you are. I.e., they treat it like a password that only you know, and so if you can recite it to the telephone help desk person, then the help desk person is assured that the voice on the other side of the phone must be Mr. X who has SSN YYY-YY-YYYY.