Sprint and Google have been very friendly recently[1], so it could just be an exclusivity thing.

What I'm more curious about is why none of Sprint's other, more recent Android phones have NFC in them- I just picked up a Photon yesterday sans NFC, and I'm led to believe that the EVO 3D and the Epic 4G Touch don't have it either. (Which is particularly weird for the E4GT, because the other Galaxy S II variants in the US actually have NFC in them. Who knows.)

[1] See the tight Google Voice/Sprint integration, the existence of the Nexus S 4G, etc.