Lots of countries use the SSN equivalent as a public ID and sometimes have for decades now. The Nordic countries, for example, often require it on any application that requires your real name. I, as an academic, just put in a grant application to a private foundation, and my number was required there like many other places.

In the US, leak of SSN apparently can result in identity theft and so its public use can seem especially troubling, but other countries use different secrets and processes for identity.

yea, in the US, we use the SSN or the last 4 digits, as a security question, which is why it can lead to identity theft

the goal would be to stop using SSN(4) as a secret