點解外國CD既日本版先有bonus track?

Because the Japanese people like to change their CDs after they get into Japan , and add thie bouns songs into the Cds , so more people will buy it. And that kind of CDs that include the bonus track is called the "japanese version".
And they will also add the music videos if the original ones don't have one.

Hope I can help u la~

我嗰d碟唔係日本版都有wo
唔一定嘅
只有日本方面喜歡