It is funny the author chose Denmark as an example because Greenland is technically a territory of the Kingdom of Denmark, and with Greenland included the Kingd

It is funny the author chose Denmark as an example because Greenland is technically a territory of the Kingdom of Denmark, and with Greenland included the Kingdom of Denmark has a population density of 2.68 per km^2. Does this mean it is not worthwhile to build public transit in the European part of Denmark? If not, then why does the population density of the entire US matter in a discussion about Tennessee, a state 80% denser than the American average? By the way, Finland has both a smaller economy and a way lower population density (18.4 per km^2) than Denmark and the US. Would railways be not useful in Finland because of that?