I agree logically that discounting dollars will make it a credit system similar to the credit system you already have.

Practically though I think people derive comfort in familiarity, even though dollar credits / cost are unintuitive in mathematical terms, people use dollars daily, even people who don’t use USD daily know the conversion from local cut to USD. And it makes the cost look really small, for example “0.5 cents” per document seems more familiar than “1 credit” per document even though the cost might be the same.