As for why the region-by-region setup probably because its a big country and patients can't travel from one side to another. Also its difficult to change because any change results is someone having increased wait time. And some of the states don't like to share their organ streams with others. The reality is those states with larger organ pool is because more people die there for whatever reason.
I've also been told that only a small percent of deaths result in viable organs for donation. I think like 2 out of 1000 is what a transplant coordinator told me.
Time is the key here, the more time the organ is not in a living body, the less likely it is to survive transplantation. So if we didn't have regions, and you were living in San Fransisco and a kidney came from a dead biker in Florida, the likelihood of the kidney surviving is less than if that kidney came from Sacramento.
And not all of a donors kidneys are ok two of us got called and only one kidney was viable.
https://abcnews.go.com/Health/Economy/story?id=7902416&page=...
The short answer is you technically can but the ethics are foggy. On the one hand you do help even out the geographical disparity. But you're kind of buying an organ that would have gone to someone else who's probably poorer than you.
As for why I haven't tried a shorter wait region, I consider transplant as not a cure. It will eventually fail. And there are other things in progress like the UCSF artifical kidney, gene therapy research, better anti-rejection drugs. My hope is when my transplant does fail, one of these alternatives are further along. So I look at each of these things as stepping stones to extend my life.