Zynga bet on being able to build out their own datacenter cheaper than what it cost them on AWS. They took this experiment very far and ultimately couldn't beat AWS. There're a lot of hidden costs when you consider AWS-level datacenter management vs. the type of comparisons you might be used to looking at simple dedicated hardware vs. AWS offerings.
Zynga's case was more nuanced than that story leads on. Zynga built out its datacenter capacity assuming a base line of users, which in hindsight, was optimistic and left them with significant excess capacity and costs.
Random Google result about this: http://readwrite.com/2015/05/12/zynga-data-center-amazon-aws...