Chökyi Drakpa says:
The preta realm is destitute of food and drink, creating hunger and thirst. It is a grim place of rocks and charred tree stumps, where the words ‘food’, ‘drink’ or ‘comfort’ have never even been heard.... Since these pretas do not find anything to eat or drink for months and years on end, their bodies are emaciated like skeletons and they lack even the strength to stand.... The principal cause [for being reborn there] is being miserly or greedy for wealth and possessions.
In a psychological sense, the hungry ghost realms exist wherever people, though immensely rich, are never satisfied, craving to take over this company or that one, or endlessly playing out their greed in court cases.