No offense, but it might have to do with the way you seem to strangers. You get a sense of a person and sometimes you feel that you can talk to randoms; that they're interested and/or you're on the same mental wavelength. These senses are important, because even in the USA, where talking to randoms is common, you still want to avoid "bothering" people. So there is still risk of inconveniencing someone with an unwanted conversation, or making them feel uncomfortable, and this is still a big social no-no.