Game mechanics are obscure. But it seems that suppliers have point to point contracts with buyers (other industries or towns) rather than delivering cargo to anywhere, where it is demanded. This means that you have to figure out where a supplier wants to deliver to and then set up lines accordingly. Suppliers seem not to start to deliver, because a line is set up. This only is the case when a new road or track is built for the line to be, which connects supplier and buyer in an efficient way, that was not available before. Suppliers can also have several buyers. But the criterium, of how much is delivered to each of the buyers, is obscure. Distance? Demand of produced goods? This obscure criterium would explain your one piece per year deliveries, contrary to none at all or a lot.