That's almost certainly because Google searches are significantly more likely to indicate purchasing intent. That means advertisers will pay more per search than per timeline view.
Yes and for an advertiser a click through from Google is far more valuable than just a view on Twitter or Facebook. The latter is more of a brand building advertising. Google's is immediate revenue so advertiser is likely to pay more.
To be fair, this is CPM, not CPC. So the click vs view thing is already accounted for.