This was a great read. As an American who is currently living in France, I'm always blown away by how easy it is for me to get just about anywhere via train.
America is way less dense than France and Europe at large.
Only in BoWash such an high density network would make sense
Almost 2/3 of Americans live in states with population density comparable to Europe. The real issue is that the density is too uniform to make rail a viable form of transportation. If you take a major American city and the surrounding suburbs and drop it in Europe, it will likely cover several cities, their suburbs, and rural land between the cities.
As @jltsiren noted, this is a false equivalence. You need to compare the population densities where most people actually live, not overall density. When you do that, a very different picture emerges.
I don't think this argument really holds up in a world where China built twenty-eight thousand miles of HSR in two decades, a lot of it connecting disparate urban areas much like what the US has: