This article argues about increasing organ donation by presumed consent and allocation priority:
To promote organ donation, legislating the principle of priority provides a strong incentive by signalling to people that registering as a non-donor decreases their chance of receiving a donated organ when needed. Such legislation is in place in Israel and Singapore. Singapore has experienced an increase in the number of donors after introducing a priority system, although the effect of the priority system is unclear because a presumed consent system was implemented at the same time. Preliminary results in Israel, which does not have a concomitant policy of presumed consent, are promising, showing a significant increase in both deceased and living organ donation.
So, both Israel and Singapore show that a priority system (that favors those who explicitly registered as donors) tends to increase organ donation.
I am wondering why this principle is apply in so few countries considering its benefits.
Question: Why is the principle of priority so rarely used in relation with organ donation?