It would be hard to create truly "functional" hardware. A piece of hardware is a real physical object with an internal state which is shared by all accessors and which can change over time. Shared, modifiable state is the exact opposite paradigm from the one that pure functional languages use.

I think this is also why pure functional languages are so hard for "normal" people to understand -- their basic premise is the opposite of the real world around us that's filled with stateful physical objects.