One reason for this revolution is explained by Etsy in terms of Conway’s Law:
When a team makes a product the product ends up resembling the team that made it.
I’ll extend this notion to say the team and thus the product end up resembling the underlying technology used to make it. When you change the underlying development infrastructure, by moving to a cloud, you are bound to change teams and processes they create.
(Full Story: Startups are Creating a New System of the World for IT)