It is not just digital assistants, but so many other things like Google maps, e-commerce sites, address auto-completes etc seem to assume that I want the North American one with a population of 300k that no one knows about, not the one that everyone has heard of with a population of 9 million.
I've always just pegged it down to the usual cultural-blindness that we come to expect from SV companies that there isn't anything beyond north America (e.g. "global launches" only being for USA, Canada, and Costa Rica etc) and that if your language is "en" then you must be American or Canadian with everyone else being funny foreigners that "we don't support, sorry"