first turn on the display of cargo ob the map so you know the site is producing any cargo at all.
Second, you must make it preferable to use your services by collecting goods often enough and transport them faster to the destination then it is by walking.
The game system is bad. No cargo in the world walks by iteself. And the site producing the goods have only that many workers. So it seems the industries are asking unemployed vagabonds to do the carrying and there seems to be an endless supply of them.