It is because short sea does not beat the delivery times or costs of rail or road in the USA, or combinations of those factors. It ain’t changing anytime soon because of hard baked into the cake policies that keep fuel cheap and road use in the USA free or very low cost compared to EU (where I generally live). As it is, this is the way it is in USA
If you can slap a container on a double stack car in Norfolk or Savannah and have it in the yard at Chicago in 36 hrs, you ain’t gonna fool around with shuffling it on a boat. Or a container of TV’s loaded on a train in LA / Long Beach and arriving at a Walmart in Lexington, Kentucky +/- 15 minutes of a known pre-agreed time …. You ain’t gonna mess with a ship, a barge and a bunch of kerfuffle.
But those factors we reviewed in depth like back in January 2017… so yeah, give up. It is like talking about trying to breathe underwater when we have lungs and not gills. No future in it.