If you want to take a train to Idaho from Boston, sure, but nobody would do that. And for NY->Boston, it's plenty dense. Freight traffic is miles ahead in American than in Europe, and is always prioritized over passenger trains - that's the reason.
As far as Amtrak is concerned the laws say that they are to take precedent over freight BUT that is not what happens on a regular basis. The rail owners never get in trouble for it.
