Not to fight this battle with you in the comments, but a) you only get two kidneys but bone marrow is, like blood cells, a replenishable resource and b) it is absolutely, unequivocally the case that paying people for blood, plasma, and gamete donations (all of which we do, but we're circumspect about saying so) increases the amount of people who are willing to participate in blood, plasma, and gamete donation.

The biology of plasma is different than the biology of bone marrow, which complicates things considerably, but the biology of plasma did not solve the plasma problem. We used to have plasma shortages, too, because plasma donation is inconvenient and strikes some people as "icky." So we increased people's willingness to engage in it by using our traditional method of encouraging inconvenient, icky things: we paid them money.