As for any species that demonstrates this behaviour, the benefits have to outweigh the costs in order for the trend to take place. In humans, cannibalism is directly related to culture.

For the greatest part of human history we were starving scavengers. We sucked at hunting and thus we incorporated stealing leftovers and utilising them the best way we could. This is also how cooking came into place. Not only we were increasing the nutritional value, we were also making somewhat spoiled food, eatable again by removing lethal toxins. Dead humans were almost ideal for our survival.

Eventually, these trends were observed to be efficient and thus they carried an almost magical explanation to a clan's survival. This is how cannibalism became ritualistic and in some instances the religious norm. It didn't prevail because eventually, the costs outweighed the benefits as human societies became more and more efficient in producing food. It is more evident in tropical climates, because in our comfy "fertile crescent" we are able to domesticate animals and preserve food much easier. They on the other hand, have to hunt for food daily, leaving little room for anything else.

If you are interested about anthropology and how human societies came to be, do read the book "Guns, Germs and Steel". There is series documentary as well on youtube. You will be fascinated.