On the other hand, as the developers have said, CORE isn't balanced for those difficulty levels.
For instance, there are a lot of 'economic' and naval construction events that inflict an off-map supplies drain. The purpose of the drain is to reflect industrial capacity dedicated to doing something that doesn't have direct, tangible consequences for you yet, like setting up a synthetic oil plant.
The problem is that all those events are based on the assumption that your country starts with the number of IC that it would have on the Normal difficulty setting. On Hard or Very Hard you have fewer IC, and you may not be able to deal with the consequences of the supply drain.