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.