Hearts are less expensive because they're easier to damage. I tried to find you more articles about this topic, but many of them have been 404ed. Here's the rest:
https://psmag.com/economics/nancy-scheper-hughes-black-market-trade-organ-detective-84351
http://www.weeklystandard.com/xinjiang-procedure/article/610145?
I just read that. I don't think they are that easy to damage. The reason why they are easily damaged in that situation is because the bodies were shot.
I think you're right. It's a fascinating topic no matter how you look at it.