It’s not that economics is hard to understand, it’s that it requires the participants to reason about their actions.
First problem was the coins. To buy something the dwarves had to haul the coins to the seller, one at a time of course. And then when given change they had to haul the change back to their room. One at a time. And the merchant had to haul their new coins, one at a time, to their room. But that was an easy problem compared to the real difficulty.
The other problem was balancing incomes with expenses. Everything was just assigned arbitrary numbers, and those numbers were fixed. So in one player’s fort they were building a huge mega construction out of glass blocks and so the glassmakers become wealthy beyond the dreams of avarice simply because so many glass blocks needed to be created. But the weaponsmith was only ever asked to create ten battleaxes for the single squad of military dwarves so he went broke. After all, everyone had to rent a room and eat. Prices need to depend on scarcity and the need to eat as much as on the labor needed to create an individual item. The weaponsmith might have earned more income for a sword than the glassmaker did for a glass block, but that didn’t help him in the long run.