Not only have quite a few companies and organisations successfully completed huge, ambitious, forward-looking projects; but Google haven't, at least nothing remotely comparable to the actual moonshot they happily co-opt. Google has done lots of amazing stuff, but usually in a remorselessly incremental way.
Gmail and Google Maps (especially Street View) are the closest I can think of to "moonshots" in that they were big and bold improvements over what had come before. But neither one would be called a "moonshot" by Google X standards. In each case a back of the envelope estimate would be enough to show that it would work out (in technical terms, if not business terms).
So why does Google act like they're uniquely qualified to make moonshots work?