Giving registered organ donors priority on organ waiting lists, as has been implemented in Israel and Singapore, provides an incentive for registration and has the potential to increase the pool of deceased donor organs. However, the implementation of a priority rule might allow for loopholes—as is the case in Israel—in which an individual can register to receive priority but avoid ever being in a position to donate organs. We experimentally investigate how such a loophole affects donation and find that the majority of subjects use the loophole when available. The existence of a loophole completely eliminates the increase in donation generated by the priority rule. When information about loophole use is made public, subjects respond to others’ use of the loophole by withholding donation such that the priority system with a loophole generates fewer donations than an allocation system without priority.
Its usually bloody moronic religious reasons why people don't like doing this. I quote this time from Judaism
While the Israeli legislation mitigated this particular type of gaming, it introduced a different loophole in the organ allocation system. One of the reported motivations for implementing the priority allocation legislation in Israel was widespread concern over free riding by ultraorthodox religious groups. These groups generally do not recognize brain death (i.e. when the brain ceases to function) as a valid form of death and consequently oppose providing deceased donor organs.5 Members of these religious groups do not oppose receiving organs, however, even those recovered from brain dead donors. It has been argued that this group of explicit free riders—those who will accept organs but not provide them—is a major factor for the historically low rates of organ donation in Israel (Lavee et al. 2010, Lavee and Brock 2012). The priority allocation system was meant to minimize this free riding by rewarding registered donors and giving free riders lower priority on waiting lists.
Nevertheless, the implementation of the Israeli priority legislation created a loophole that may allow this type of free riding to continue. The Israeli donor card gives a registrant the option to check a box requesting that a clergyman be consulted before organ donation occurs (see Figure 1).6 An individual who wants priority but does not want to be a donor could check that box with the implicit or explicit understanding that his clergyman would refuse donation if the supposed “donor” were to die and be in a position to have his organs recovered.
Ridiculous and because of these loopholes, the rate of organ donation is seriously low in Israel.