I hope you realize this wasn’t meant to be an accusation, just a more general observation.
I usually assume that the stories I read are set in the US with American characters until presented with evidence to prove me wrong. I went for years reading For Better or For Worse, the famous Canadian comic strip, before someone drove to London and I realized that meant London, Ontario! Authors can drop hints that other Canadians notice, but some of us need a sledgehammer to the head! ;-)
With stories set in the UK, the spelling is usually the first clue. With Aussies, the language is the giveaway – so much unique slang. In visual media, cars on the ‘wrong’ side of the street do the same thing! ;-)
Most of us are guilty of profiling people based on visual cues, others on audible cues. It’s human nature – historically vital survival skills. But we’re not dealing with potentially violent (animal) predators anymore. It is possible for society to change – left-handed people are no longer thought to be evil, blonds are not assumed to be dumber than the rest of us, and redheads aren’t seen as more likely to get angry easier! But clearly it won’t happen overnight… ;-)