They say that they're unreliable in supply, that the ocean rates fluctuate, and they gave various other reasons. The quandary we're left in is that most of our non-board grains that go through the port, which comprise about 35% of the grain, are carried almost exclusively in salties.
The grain companies don't seem to have a problem getting the saltie supply for their own crops. Very little, if any, of the Wheat Board crop goes by saltwater vessels.