even if musk's calculations in cost were correct that 6 billion for one route between LA and SF. what's nice about airports is that they can service between any two airports, regardless of distance, so long as your plane has the fuel capacity to make it.
so you're sinking 6 billion for just one route. of course... that was before NASA said it would need to go slower, and have significant changes to the design of the capsule in order to work... and other engieers decided the size of the capsule which needed near vacuum had to be roughly double in diameter... and that would be if a private entity built it. so lets say 40 billion dollars for one route. not to mention being millimeters off (which as the ground shifts will happen) will cause the people traveling at 6, 700mph insider a sealed windowless capsule that itself is inside a sealed tube to be uneasy as it shimmies and shakes and vibrates and they'll hate it and no one will use it.
trains are an awful idea. i don't know why people keep on trying to push them. people who spout this nonsense are almost as horrible and soulless as vegans.
now yes, for small areas subways and light rail can be great. i have used subways in DC and NYC and they are perfect for getting around. in NYC i'd agree, only an asshole would bring a car into manhattan... a very rich asshole. everywhere else though in this fine country of ours? cars are necessary. in my twin cities? there are two light train lines. i used to live a block from one of the stations, and i've used the lines twice in ten years, once, to go to a baseball game, and another time to drop my car off and it took me to the start of my marathon race and then it took me back from the end after a series of bus switches which was fine