The Nexus line was never meant to sell initially. (Hell, the reason the injunction on the Galaxy Nexus was lifted is cause it doesn't) They created the phone for developers and to showcase the latest version of Android. It was never meant to appeal to the average consumer, and that's why the original Nexus was sold exclusively through Google when it first dropped. There was a decent amount of Sprint/Verizon CDMA users that wanted in on the action, so they decided to drop it for the carriers as well. The carriers could care less about the device since it removes all of their beloved bloatware. Like it was said before, the carriers are trying to do numbers, so they could give a fukk about releasing updates when they can get you to throw down $200 or more to buy a new phone.
That's starting to change now since the release of the Nexus 7. They need to just drop all of their flagship devices on the Play Store exclusively while undercutting the carriers. Who the hell needs to buy a phone from a carrier in 2012? They have the potential to change the way people purchase phones/tablets from this point on, they just need to market it right.