DO has a nice product for relatively unsophisticated users that just want to build a website. But when you want to move a large application that spans hundreds or even thousands of servers and scales up and down to meet demand, you're not going to run it on an unsophisticated provider.
You're going to want a provider with rich service API's and enough capacity to let you scale your infrastructure as needed.
Most of DO's customers are not in the target market for AWS or GCE - while those users provide decent revenue from a small amount of compute resources, Google and Amazon are looking for the larger corporate customers that are willing to purchase thousands of compute units and terabytes (or petabytes) of storage.