1) They are dependent on Intel or AMD for the higher end processors. This is a $5 billion-per-factory industry. So that is one thing they can't easily replicate.
http://www.informationweek.com/cloud/infrastructure-as-a-ser...?
They don't make that on AWS, in gross revenues. This is similarly true of most hardware inside a modern server. They can make small improvements but they can't magically take over the CPU market or any of the other core components in a 'big way'.
2) Creating all that in-house software automation is complicated, difficult, and expensive. This software isn't a requirement for in-house hosting.
So they need to crush the margins of their supplies [power; bandwidth; hardware] to the point that they can get their own margin on top of that + cover the cost of a bunch of custom in-house software development. For a stable workload...that just isn't going to happen.
AWS isn't going to cut their prices 33% after the largest price cut I've ever seen them make in April, let alone the 67% they'd need to.
Sure, in 10 years, they might manage it. I don't see it happening faster than that.