The carrier paid for it. They want you to sign up for a contract extension to get the shiny new phone. They have no interest in supporting your old phone.
And who paid the carrier? I pay AT&T upwards of $3000/year, and when I upgrade, they still charge me $100-$200 for the phones I want. I'm pretty sure I'm paying them for that.
I bought an unlocked iPhone. What does that make me?
And this may be why our society is getting screwed.