Wow, in most cases this just isn't true. Granted some employees are ordered to use it as a greeting, but most people who ask genuinely care, and there is no social expectation to ask. Perhaps the culture in the USA is just a bit more personable than you have a theory of mind for? If you really don’t believe me, try answering the question in the negative, theres a reason why its like a joke that you have to respond positively. You’ll instantly be asked whats bothering you, and most people won’t let go easily. They genuinely want to try to cheer you up if you aren’t doing well and if they think they can reasonably help you, generally will.