Maybe in Germany, but France has barely populated areas and yet we have one the biggest high-speed rail network on the planet. In fact, the fact that France is the biggest European country after Russia is probably the main reason high speed rails was invested on back in the 70s: the bigger your country the more you need high speed rail.
High speed rail is not going to do a lot of good in South Dakota, but we can serve most Americans with some type of decent rail without contorting ourselves. And the bar is on the floor since a lot of Amtrak is not even a single round trip seven days a week.