The question was what the train network is like outside the cities. And the answer is we don’t use trains because it is not efficient for the scale of the country. This is correct.

Most people ARE interested in coast to coast travel. It is called flyover country for a reason.

There are a few exceptions like the Baltimore corridor, or the San Francisco peninsula, and these are in fact serviced by good trains.

Train travel from LA to NY wouldn't be efficient, but there are plenty of population poles like LA to SF where train travel would make sense and a network of those could make cross country travel feasible if not in a hurry. But as the GP pointed out, it is not that useful if you can arrive to LA by train, if then when you arrive you need to rent a car before you've even left the station.

It is always shocking to me when I land at an airport in the US and there no public transport available.

It is common for conversations about good local public transport to have a retort in some sub-thread about how big the US is, as if the feasibility of long distance travel affected the feasibility of other modes of local travel.

You mention the SF peninsula. When I first moved there, I lived in the westside of SF and had friends living in Sunnyvale. On a weekend, it took 4 hs to get to Mountain View (~40miles, at the time, checking now it seems like Caltrain weekend service might have improved, so the same trip would take about 2hs), and then had to be picked up by car to finish the rest of the trip. It was faster (~3:30hs, if more expensive) to go from Paris to Amsterdam (>300miles) by train.