Because what I read about the Japanese Civil Wars. With all the assassinations of Emperor's going on. And all the backstabbing that can literally be compared to Game of Thrones. I find it hard to believe that they actually had so much honor.
Not to discourage other answers but, there is a good answer in the FAQ about this from /u/bigbluepanda
https://www.reddit.com/r/AskHistorians/comments/4rte1l/were_samurai_generally_honorable/d54202b/