Because contrary to popular belief, American English is not the first, only, or de facto standard language in the universe.
Just dicking with ya. Of course for most scientific terms, English or German tend to be the preferred languages that most other idioms inherit from (with some exceptions during the 19th and 20th centuries when France set the bar for many fields of study), and indeed even the actual word "byte" is the same in Spanish and English, as is "bit." I have no idea about the Spanish etymology behind either, to be honest, and I cannot speak to the other language families. Even German and Dutch nowadays seem to be following the English conventions, using variations on their Grecian/Latin counterparts.
