I highly doubt they care about the updates. It's time, manpower and wages for an update to a phone people already have. What are you going to do? Just walk away and get a new phone somewhere else? That isn't remotely cheap or practical.
Software update don't make carriers money, new subscribers do. Until the OEM's put their feet down and demand more timely updates it's only going to get worse. Either Google needs to take better control of the update process and pressure the carriers or someone like Samsung needs to say 'Get it together, get the updates out, our you won't see another Galaxy phone on your network for years.'
I don't see either happening anytime soon.