The vast majority of the population lives near the coast.
Why unload goods off boats one thousand miles from the border and truck them into the middle of the country where they need to be trucked to the coast.
Fedgov.con is screwing the American people
The same primary factor that drives this entire scheme, and the entire export of US jobs and industries: cheap labor, cheaper port labor, cheaper port operations in general, and cheaper truck drivers to move the goods away from the ports to points all over the US (with Mexican drivers all the way).