Companies need to make more money. If it's a publicly traded company, then a continuous increase in revenue generally makes the shareholders happy. And despite a neck-breaking soar to high stock prices in the past year, Google has suffered some slowed growth in recent months. With text ad growth slowing, it's time for Google to find new ways in which to make more money.
Google hasn't been sitting on its laurels--it's dabbled in widget ads, and video ads, among other things. And now, it may be moving towards image ads that appear alongside image search results, according to a Bloomberg report. This seems to be a simpler way in which to increase ad revenue, as it follows some of the same principles used for text ads, and will generally seem a familiar occurrence for the widest user set.