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.
Possible but I do wonder if this isn’t a fallback.
E.g. use resource values but in the edge case where there’s no logistics in/out then we need to allow you the basic ability to fix that. Build roads/bridges/ports to rectify it. Ideally you’d do this so the city can operate at a barebones level to make that happen.
If so seems like the kind of thing you put on a degrading curve. So at first it covers hiccups (cut off all input/output lines such as bridges temporarily unavailable) and helps with computation instead of having to “real-time” calculate every item in/out. It’s easier to just let you aggregate in time intervals throughout the day.
Then if that state continues you start impacting the “production” of those businesses internal warehouses down to 0 until the city is basically dead and it’s “game over”
If they did something like this the bug could be improperly applying that curve and so it isn’t scaling down.