Only the major yards are gravity-"powered" hump yards (the gravity does the sorting part, but a locomotive still has to push the consist up from the other side as they're decoupled). Most yards, the smaller yards trying to serve the last mile, are flat and require manual sorting with a locomotive, and often while blocking the rail line to all other traffic. Plus, they often can't sort the cars into the ideal shipping order because of dynamics in the train. One of the worst ways to order the cars is with autoracks (automobile carriers) up front and tank or steel coil cars at the back. Autoracks are very light in comparison and have long-stroke draft gear (coupler cushioning). Just slamming the brakes can cause a derailment with that arrangement with column buckling of the train. Or worse, lots of cars only ever get loaded in one direction, such as autoracks and tanks, so they're empty and even lighter on their return trip. They have to sort heavier cars towards the front or else they risk stringline derailment on curves while pulling.

Yes, we're aware they need to do the first 99 miles to get to the last mile problem. The problem with rail, as defined by the market, is that trucks do the whole 100. And while yes, the majority of consumer goods rail traffic spent 2 months on the water, the majority of containers were not ordered for the end user or final sales point. They're warehoused at distribution centers, waiting to refill other DC's needs. Even Amazon is running full intermodal container trains across the country. It also completely ignores the vast amount of domestic/continental raw goods such as oil, lumber, vehicles, metals, trash, scrap, grain, plastic pellets, lethal chemicals, coal, and, apparently, orange juice.

And I say this as someone that votes for trains. PSR does not solve much. It's a buzzword for hostile takeovers by investment companies that have no intent on improving infrastructure. It brought some improved shipping status decades later than every other mode of carrier.