Google is constantly changing the way they index the web. The Google algorithm updates have come along way since the beginning. They have successfully created a service that weeds out most black hat tactics and generates the content/sites you are actually looking for.
Google is fantastic at recognizing the flaws in its system and quickly developing strategies to fill the gaps to deliver the best, most relevant results. The recent mobile update is one of Google’s biggest changes yet. If your website is not optimized for mobile, you need to make these changes ASAP.