Don't forget geography, and by extension type of freight. The United States doesn't have a lot of navigable waterways, and none go east-west. This means that a

Don't forget geography, and by extension type of freight. The United States doesn't have a lot of navigable waterways, and none go east-west. This means that any bulk goods you want to transport have to go via rail. There is no other option. As a result the railway network has been optimized to do bulk transport at the lowest price possible, even if it means sacrificing speed and quality. After all, coal doesn't care if it sits in a siding for several days. It's true that the US is shipping an awful lot of tonnes via rail, but this doesn't say anything about its ability to ship regular goods. Getting a single wagon from point to point in a timely manner is significantly more complicated than doing the same with an entire train.