The rail line would have exclusive right of way for this traffic. Gotta' be dirt cheap!
Another source of income (investment?) for FARC!
The big trans-Pacific container ships save lots of time on shipments to Atlantic ocean ports and and containers headed to various North or South American or even European destinations could be loaded on to different ships at the terminus port.
I don't know a lot about international logistics, but on the surface, this makes a lot of sense to me.