
This is primarily happening due to the overall fall in the advertisement rates given by the advertisers. In the second quarterly report google mentioned that "Advertising rates, or costs per click, have headed south as users gravitate to smartphones and tablets, where Google can generally charge less than on desktop computers.The cost per click for online search ads continued to decline in the second quarter, falling 16% year-on-year but the overall number of clicks on ads, however, increased a robust 42%."