"Prefer" is a stretch. It's not like consumers were presented with a choice between two carriers that were similar in every way except that one went with the subsidized model and the other did not.
The choice consumers had was either a crappy carrier, or one which forced you to go with absurd monthly plans.
Additionally Google did try to disrupt the cellular companies a little by selling their phones unlocked through their own webstore, but the American market didn't buy them. Yes there really is only one network that gave you a deal if you did this (T-Mobile), but Americans seem to prefer subsidized phones with absurd monthly plans rather than paying for the phone up front and being free to choose the network.