Zapping water with electricity isn't very efficient. As I recall, you only recover 25% or so of the energy you pump into the water to spit the molecule.
Also, there's almost no vehicles out there that use fuel cells. Billions use gasoline, though.
This might be the answer for "how the hell do we access all that cheap wind and solar power in the Midwest and Southwest?"
Wind turbines and solar arrays turn air into gasoline. We fill up tanker trucks and let the Midwesterners and Southwesterners burn air-derived gasoline. Tens of millions of people will begin burning "renewable" gasoline.