I don’t know what to call them, kind of an in between between what you would call fast food and what you would expect from a “slow” fancier restaurant
Fast casual? Typical chains considered to be “fast casual” are Chipotle and Five Guys. A local taco/burrito/burger/sandwich place would probably fall in that category.
Because the US doesn’t have a federal identification card. At the state level you can use the id number of someone’s drivers license or state id for identifying them, which is marginally better since it changes with new id cards.
SSNs weren’t intended to be used for identification, but since there’s no other national option they effectively are.