According to Google Trends, "Cloud Computing" began picking up popularity in early 2008. As people became curious, more were searching the term and the curiosity peaked around mid-2011. Since then, as the Cloud became a standard part of technology, search trends also began to even out but have hardly disappeared.
There are a number of reasons that we may have seen these trends over the years, and they all relate to how the technology has progressed. This infographic from Sonian Is a very nice summary of the complete history so far. It takes you through the Big Cloud Moments, Changing Cloud Perceptions, Cloud Growth and Adoption, Terminology and its Pioneers.