The Bank for International Settlements has issued a rather stark report around this question: "Why, almost a decade since the Great Financial Crisis (GFC) does the global economy seem unable to return to sustainable and balanced growth?"
 
This is the PowerPoint from that report, delivered as a speech by Claudio Borio on Feb. 10. I think it has more than enough meat to give you the gist of the idea. Get through the exec summary at the beginning at the very least.