Why would they possibly want to cut into their profit margin?
What is baffling is why the public hasn't demanded it.
The points in this article are pretty persuasive.
Cash for Kidneys: The Case for a Market for Organs
In 2012, 95,000 American men, women and children were on the waiting list for new kidneys, the most commonly transplanted organ. Yet only about 16,500 kidney transplant operations were performed that year. Taking into account the number of people who die while waiting for a transplant, this implies an average wait of 4.5 years for a kidney transplant in the U.S.I think the squeamishness on "moral" grounds are pretty much a smoke screen. A good number of people have no problem with the free marketing of death in the form of abortion clinics nor choice when it comes to deciding on what to do with their body for the same. So why should an adult deciding to be compensated for their organs to be used in transplantation be any less of a right to "my body,my choice"?
The situation is far worse than it was just a decade ago, when nearly 54,000 people were on the waiting list, with an average wait of 2.9 years. For all the recent attention devoted to the health-care overhaul, the long and growing waiting times for tens of thousands of individuals who badly need organ transplants hasn't been addressed.
Finding a way to increase the supply of organs would reduce wait times and deaths, and it would greatly ease the suffering that many sick individuals now endure while they hope for a transplant. The most effective change, we believe, would be to provide compensation to people who give their organs—that is, we recommend establishing a market for organs.~snip~
At least in this case an argument can be made that lives are being saved and health improved.
Protections can be built in to give the donor an opportunity to truly consider what they are doing but in the final analysis what it truly comes down to is "my body,my choice".