Comment by hnfong

I think the reason was that in the early days of the Internet, people absolutely detested the idea that any entity related to the government (eg. your post office) could know who you are and your personal particulars.

So everything developed in an ad-hoc manner. E-commerce web sites just asked for the information they need (and the information they didn't need), those who were comfortable using those websites used them, and the paranoid probably held out for much longer (and rejecting the idea of centralized auth loudly).

Most attempts by private companies to establish some de-facto identity/auth/login service mostly failed (well, the couple Big Tech companies got somewhat close, but none of them got close enough to be able to get other sites to use them exclusively)

Besides, even if there was some protocol to handle the payments and shipping without sending the info to the seller, you'd have to trust the payment processors and the postoffice to be secure. It's basically a choice between whether you want to put all your eggs in one big basket or spread them around somewhat.