It’s all the same 20 minute agent.
That’s true, and it’s actually rather perverse. You have industries sitting on the map doing nothing but waiting to be hooked up to customers, but if you give them a line that’s too long they’ll stubbornly sit there at zero production. Who owns those businesses that are sitting there doing nothing?
On the other hand, sometimes you have symbiotic industries that just happen to be sitting next to each other so your map will show that a forest just happens to be supplying a sawmill which is sending goods to a nearby town. In these circumstances it’s very difficult to ‘capture’ these goods onto a line to another town because the industry naturally prefers the shorter road route to the local town – only by putting enough trains on the line to reduce frequency can you compete, and even then if the line is short enough that the travel time is low.
I suspect that once a town’s demand is satisfied the industry will upgrade if you’ve made other demand sinks available via lines, but that takes a significant amount of time during which your line and trains are sitting there costing money with nothing to carry. The game needs a system where industries can indicate that they would like to have a line to a particular destination to give you a clue as to where there is demand to satisfy.