The point is that users should be in control of their data, which means they need an easy way of accessing it. Providing an API or the ability to download 5,000 photos one at a time doesn't exactly make it easy for your average user to move data in or out of a product.

At Google, our attitude has always been that users should be able to control the data they store in any of our products, and that means that they should be able to get their data out of any product. Period. There should be no additional monetary cost to do so, and perhaps most importantly, the amount of effort required to get the data out should be constant, regardless of the amount of data. Individually downloading a dozen photos is no big inconvenience, but what if a user had to download 5,000 photos, one at a time, to get them out of an application? That could take weeks of their time.