Yes, the US is big, but a large part of its population is heavily concentrated. Trans-continental high-speed trains would be a waste, but better connections on very densely populated areas would be a great idea.

And the difference is not really that stark as you make it sound. Europe can be big too. While only 8 US states have a higher population density than France, there are 35 US states with a higher population density than Sweden.

https://en.wikipedia.org/?title=List_of_U.S._states_by_popul... https://en.wikipedia.org/wiki/List_of_sovereign_states_and_d...