I would also argue that it's because Sprint isn't pushing it. It was never *really* featured on their site, and in stores, I can't them to talk about it. If I go in and say, "what do you think of the Nexus S" (which I have done three times now), the responses I have recieved are.
1. The Evo 4G is coming out soon (asked about a month ago)
2. Check out the Evo 4G (two weeks ago)
3. Check out the Evo 4G, or the Photon which is coming out (today)
Clearly there is not corporate initiative to sell it, which I'm guessing is based on:
1. No Sprint bloatware to tempt people into getting Sprint TV upgrades, etc.
2. Free tethering
But going back to the original question, because Sprint is not pushing it, not many people are getting it, which means that people aren't writing about it.