Not only that but programmers become used to using American spellings in identifiers. That can can come through in online communication simply through muscle memory. I even have problems typing 'with' without my fingers automatically making it 'width'.
Note, non-exhaustive hypotheses. I've lived in England my whole life, but I've done a lot of talking to Americans online. I don't think I'm consistent with my locale, because I don't care enough to pay attention. (Also I don't even remember which of -ise and -ize is which, despite occasionally looking it up.)