Im-/Export bug, hints, symptoms and causes - "All resource management in the game is a deception."
forum.paradoxplaza.com
TLDR: If you expect the in-game economy simulation to include features like supply chains, exports, and imports of goods, and resource processing, it doesn't. Here are the main issues: First Part: Your city doesn't generate a 'demand' for goods...

Big if true.

Response from the Devs included, they’re claiming this is just bugs which I really hope is the case.