They might have an accomplice within carriers' or dealers' employees. Imagine how many shops are there across the country and how many employees have access to reissuing SIM cards. As an excuse such an employee can always say that they didn't notice that the documents were fake.

at least in germany ordering new sim cards to new addresses your provider never heard of before was a thing some years ago. I think porting a number is a lot easier if you know the detailed process though.

Oh, my bad, I thought US was the exception

Here in Italy you must provide your ID card and wait a couple days for the carrier to check the data. Goverment websites even use 2fa as a proof of your physical identity

Why is it so common for some people to use "EU"/"Europe" when talking about a quirk about their country? Americans do it too, though the states are far less unique than countries.

Because many of the rules are made on the EU level, not by the individual country.