Ok, so say I do fall into that small percent that has complications after donating. Say I even end up dying from it. Do you think my wife and kids are going to care that I saved a stranger's life at the cost of my own? No. They would much rather have me alive and healthy than some random person who lost the genetic lottery.
And that's the point you are failing to grasp. I don't care if some stranger dies because they can't get a kidney. Now if said stranger is willing to compensate me an amount that will allow me and my family to live comfortably for the rest of our lives, then I'd be happy to give my kidney.
And that's not me being greedy. The reason I'd want that much money is as an insurance policy in case I do fall into that small percentage that has serious complications after donating. And no, I won't refund the money if I come out of the donation just fine. That is me being greedy.
In short, you want my kidney, you gotta make me rich in return.