In most cases of human sacrifice, it was done for religious reasons, and the meat wan't eaten (or if it was then in small quantities, like eating the hearts as you mentioned). even back then, the consumption of human body parts wasn't considered healthy or nourishing, it was done only to appease the gods/give us their favor/make us stronger/etc.
I think that thoughts and stories of eating people, and especially kids that is pretty common in many societies and myths, comes as a warning or as something to fear, both because human sacrifice was common enough at a certain point, but also because it helped to easily scar people (whether the parents or the children themselves).
I think that one of the problems with eating dead humans, even recently dead people, is that those are even worst "parts" then the livings parts. What I mean is the even in the conventional meat eating industry they usually don't eat meat from animals that died naturally (and i'm assuming you're not talking about mass murder), and the reason for that is that the animal (or in our case, the human), died for a certain reason, more likely then not, from health reasons, so the chance of the meat containing disease, sickness, or even just being super weak is a lot higher then when they take a supposedly healthy animal, kill it, and harvest it.