It's mostly marketing. Even movies get different titles in different countries! It's what the manufacturer thinks will sell in a particular market. In the US, the "Rebel" name
might have been used, at least in part, to get a copyright. For instance, Intel started using the "Pentium" name, as they couldn't copyright a number (which is what they formerly used to name their processors). It also gives the consumers a "brand" with which they can identify. After all, we are a rebellious bunch!

Sometimes, it is for legal (someone else has rights to a particular name in that country) or even "societal" or "superstitious" reasons, as a particular name or number could be considered
unlucky (the number 13, in western culture, for example), offensive or downright
evil. For example, we will never see an EOS "4D" or "9D" from Canon, as those numbers are "unlucky" in Japanese: Four is sometimes pronounced
shi, which is also the word for death, while Nine is sometimes pronounced
ku, which can mean suffering.