You body is worth a lot of money to your estate. By donating it someone in the medical industry gets to steal that money from your family then profit handsomely from it. That’s why I choose no for organ donation, the whole industry is corrupt and I don’t want to support it, even if it means that some unfortunate sick person is unable to buy my donated kidney for 50-100k in processing fees.
But AFAIK on some countries of EU and Brazil, receiving organs is either free or inexpensive.