Space Politics has a discussion about why the public doesn't know about, or doesn't seem interested in, NASA's Vision for Space Exploration. Check out the article for the whole debate; I'll just include this anonymous comment that invokes NASA's Space Prize program as part of a potential different implementation of the Vision than the one that is happening:
"NASA is obviously not a private sector organization, but the agency’s human space flight programs could do a much better job harnessing lean, mean private sector innovation and competition in highly visible ways, even if the agency wasn’t sending astronauts beyond LEO. But instead, we spend tens of billions of our taxpayer dollars on bloated, uncompeted, fatally flawed, government-designed and -operated systems while only paltry hundreds of millions go to competitively selected commercial human space flight services (COTS) and practically no funding goes to private technology innovation competitions (.e.g., Centennial Challenges)."
It's a mystery to ponder, although to be fair a few years ago there was no NASA Centennial Challenges program at all. However, less than one quarter of 1/1000th of NASA's budget isn't much for a series of national technology prize competitions.