These trains are over 3 miles long. This is to amortise the overhead of staffing? The locomotives and their cost scale linearly with the train, but the engineers do not?
that's part of it but not the main reason. the main reason is that if you make the cargo train too big to fit into the pull off on single tracked rail, then passenger trains have to yield to the cargo trains.
I have a grudging admiration for the sociopath that came up with that solution. Still, it has an easy fix: make it illegal to run a train that does not fit into the pull off.