There's also the matter of how long you expect to maintain certain things, and how fast you're changing stuff around. The cloud is optimized for changing things

There's also the matter of how long you expect to maintain certain things, and how fast you're changing stuff around. The cloud is optimized for changing things really quickly, where hardware is optimized for long-term cost effectiveness of relatively static assets. For example: The Obama campaign famously ran almost entirely in the cloud, because it was run like a startup that knew exactly when it would be shutting down. But the DNC runs mostly on physical hardware, because it's expected to function indefinitely.