It's asking much to not generalize, generally. Like, are you going to ask why you go on green and stop on red every time you come to a light? Not all red lights mean stop.
I think we can artificially not think of ethnicity when hearing names, but simultaneously realize people can choose non ethnic names or ethnic, not withstanding new immigrants. And, it's not clear that when people do internalize ethnicity and name associations that it results in negative outcomes. There was a recent study which contradicted previous studies when they controlled for other factors.
In any event, people make all kinds of assumptions and are often wrong, but we don't call them out because we have not become 'conscious' of them, till someone points them out.