The reason I'm not an organ donor is simple. Everyone in the chain makes money: the OPO, the hospital, the doctor, and the insurance company. The only one who doesn't is my family, but they're the ones offering the scarce resource. If there were a pre-registered organ market then I would gladly opt-in if the price were sufficiently high.
If no one else will work for free, I will not either.
If no one else will work for free, I will not either.