Stupid chart, huge difference here. Google has the advantage of knowing what a user wants when they are searching for it. Facebook is always pushing ads when users are looking to stalk people's photos.
Not to mention that Google is in the business of sending you away from their website; hopefully through an ad link.
If users are spending more time on Facebook, one could extrapolate that they are spending less time clicking on ads. The exact opposite of what Google wants.
