WRT the west coast, mostly. It's about as long as Japan, but only about half the population. It's certainly populated enough that it's not justifiable that rail travel is so slow.
Less so for the east coast though. From roughly DC to Boston is decently connected with rail, but is not nearly as direct of a corridor as Japan.
Cars were already popular in the US and good enough of a solution in conjunction with the highway system, maybe. If basic transportation is solved, it probably reduces the impetus to build passenger rail for rail's sake.
Really? Take it all the time going to NYC even though it's not really very convenient for me to get to a northern station. Amtrak is priced to make it a good idea to book tickets in advance. Shinkansen isn't cheap either, especially if you don't have a pass--not sure of current details.
It's true to some degree now. But it wasn't very true -- or expected to be true -- back when train lines were being established. That was during westward expansion.
I'm very aware! I live in NYC and have taken many trains up/down the corridor. But it still pales in comparison to the experience I get in Japan (which is cheaper, nicer, faster, more frequent, often more direct, connects up better to local transit within cities, etc.)
