Because a lot of services don't work without trust. Credit rating agencies are the Certificate Authorities of the physical world.
To give an example, a company will hand you a $1K smartphone for as little as $20. The only guarantee they have that you'll pay the remainder is that you have a history of doing so, they gather this history from credit ratings agencies.
In order for you to be uniquely identified they need a unique identifier. Even full name + birth location + birthdate may not be unique given enough data-points.
SSNs aren't fit-for-purpose. But the purpose of uniquely identifying an individual is a valid one and likely a hole that will need to be filled one way or another (and there are many good concepts to replace SSNs).
That seems like an unsatisfactory explanation. In Germany, for example, although we have a national ID card with a number, that number is almost never necessary to get a service. They seem to manage without it. The only institutions regularly demanding it are the state itself and banks.
So no, a national ID is not necessary for the purposes of creating trust.
But this doesn't seem responsive to the point. If I pre-pay for my phone and service, why does Verizon still demand my SSN and other data? Why do they even care who I am?
I bought an unlocked Android phone from Target, and use T-Mobile prepaid. They don't have my SSN, and didn't even have my name til I paid for some minutes via the website. (Now I pay by CC every month, but oh well, not real important to me.)
Cable service can certainly work without trust. Most of the services are fixed-price, and you can use your own equipment. There's no reason this can't be prepaid anonymously.
What the cable company usually does genuinely need is a physical location, which isn't very good for someone with hardcore anonymity needs like a criminal or a spy, but fine for those of us concerned with needless data leakage.
Most institutions in the UK demand a passport or driving license.
You need a birth certificate to get a passport [1]
You need a passport to get a driving license [2]
In order to vote you need a national insurance number [3], which is issued to you on your 16th birthday, via your guardian's/parent's electoral registration information.
Ergo a birth certificate is a de-facto national ID (or immigration documents)
And many many don't. It's not a requirement to have a passport or driving license to open a bank account, or to sign up with a credit agency (although many/most lenders will want some ID to actually lend to you).
I don't have a british passport, a british drivers license, but I do have a NI number. I can vote, I can open bank accounts, I can get amazon parcels, I can do normal daily things without them. The only people who have my NI number are 1) the electoral register, 2) my employer, and 3) hmrc (as far as I'm aware at least).
I've not shared it with Amazon (who are the company mentioned in the post), or with my utility provider, or with my broadband provider. I've also not given them my passport or drivers licence, and yet they all seem perfectly capable of verifying I am who I say I am, all without me having any form of national ID.
To give an example, a company will hand you a $1K smartphone for as little as $20. The only guarantee they have that you'll pay the remainder is that you have a history of doing so, they gather this history from credit ratings agencies.
In order for you to be uniquely identified they need a unique identifier. Even full name + birth location + birthdate may not be unique given enough data-points.
SSNs aren't fit-for-purpose. But the purpose of uniquely identifying an individual is a valid one and likely a hole that will need to be filled one way or another (and there are many good concepts to replace SSNs).