Don't forget the impact of hydrogen on metals: turn everything brittle. For a company founded on reusable componentry, Hyrdogen in your turbopumps, fuel chambers, combustion chambers etc. is kind of a deal breaker.
They only flew each Shuttle an average of 34 times, with months of refurbishing between flights. SpaceX wants to fly each engine hundreds or even thousands of times, with turnaround less than a day.
