The decision to build a private cloud sets back other priorities, like competing with Amazon on Grocery. It may, or may not, pay off for Walmart. If Walmart did store their data in Amazon's cloud, it is possible Amazon could use that information (sales, prices, etc) to more efficiently compete.

Conversely, if Netflix built out their own cloud, it could have come at the expense of delivering more content, which could risk unseat their position as the leader of streaming space.