I know what you're getting at, but the DMCA and carrier subsidies don't really have much to do with each other. My contract with my carrier has early termination fees and other rules that prevent the carrier from getting screwed. This is true regardless of whether or not its legal to unlock my phone.
Maybe it makes more economic sense in some cases to purchase the subsidized phone. There are plenty of perfectly reasonable use cases that do no affect the carrier's ability to recoup the subsidy and or have no other practical effect on the contract.
I understand that, but by bundling the phone with the plan and making impossible to distinguish what you are paying for the phone and what you are paying to make calls, to effectively compare two offers, or even to purchase the service without the device, they limit competition.