"Oh man, Christians are so bad!"
Your graph doesn't have any source, so as far as I know that data is completely made-up.
Let us assume it's true though: the point is that religion isn't the prime motivating factor in terrorist attacks. If it was, Christians would be terrorists too, since there's plenty of Bible scriptures that encourage war against infidels and stoning heretics. The way I see it is that blaming it on messages in the Quran is just textbook scapegoating behavior. People don't want to actually learn the complicated factors that contribute to terrorism, and so they pick a simplistic explanation that makes it easy to blanket-label a group of people as 'the problem'.
The reason Christians aren't terrorists has nothing to do with the Bible being nicer (because we've already shown it really isn't). It's because the average Christian in the modern age lives a completely different life than the average Syrian Sunni Muslim.
Also, for what it's worth, your graph shows that right-wing American extremists killed more people than Jidahists (clarification: in the US) for nearly every single year after 2001. That's not a very flattering statistic by any interpretation.