The problem with trains is that you need large signalling blocks and distances between trains and blocks for safety reasons - a fully loaded freight train can have a braking distance of well over 1.000 meters, and accelerating and decelerating them takes a lot of time and energy. Also, shunting carriages between trains takes up lots of space for the yards, a lot of time to couple/uncouple and verify the correct operation of the brakes.
The CST system seems to operate at almost zero distance between carriages, which even with the lower speed of 30 km/h should still have a greater total bandwidth than an equivalent-sized two track railway system. Also, it can operate 24/7 unlike rail systems (because of noise complaints and co-existence with passenger trains), which should further increase the available bandwidth.