Sure, the SSN is used a lot but it's normally more for things on the level of bank accounts or signing up with a new employer, where there's some serious invest

Sure, the SSN is used a lot but it's normally more for things on the level of bank accounts or signing up with a new employer, where there's some serious investment and need to validate your identity. When you enter it into a website, it'd better be for an important reason. The CPF is something you might use at the grocery store when buying a piece of fruit in the hopes of winning 1000 BRL from the government for helping the store prove that it's paying its taxes. Go to SP and every shop will ask "CPF na nota?" True, you can just answer "não obrigado/obrigada" but from what I saw, most people give it out. You just don't see that same level of usage in the USA. You're not going to wander into some store and have the shopkeeper ask for your SSN as soon as you get to the counter.