Building new trains is always great, but I'm curious why they chose to go for what appears to be a small loading gauge, thus preventing them from using shipping

Building new trains is always great, but I'm curious why they chose to go for what appears to be a small loading gauge, thus preventing them from using shipping containers. I was under the impression that containerisation and palletization of cargo leads to huge efficiencies, but surely this setup would require much more labour-intensive (or machine-intensive) loading and unloading than just slapping a shipping container on a rail-car?