That's exactly it. If you need to haul loads of stuff efficiently the train is definitely a better option. But, can't deny there's some compelling pros to this idea if it was actually feasible. The main one is that you wouldn't need to load stuff on and off the train and instead just run the trucks all the way from start to finish. Another one is re-using the existing infrastructure and vehicles. And the last one is that truck warehouses are easier to move than train stations, so they don't impede city's growth as much, but I'm not sure about that one, maybe there's some other options - I'm just salty at my homecity's planning where a train line effectively splits the city in half causing massive congestions at the few available rail crossings.