Yeah - this is why I find that argument very specious. Florida has a higher population density than France but there's no TGV equivalent running from Jacksonville to Miami

It's only one of the arguments. Florida has neither the political incentive nor the restrictions on air traffic to put pressure on government to build these things.

But the excuse is wrongly used, nobody is expecting bullet trains in Alaska or low populated places. So mostly people/politics are to blame and not terrain or density.