Its not crowded in the USA by any sane definition of the word crowded.
In a few dense urban areas sure, but that happens in all big cities, everyone wants to live close to the centre and so it gets crowded.
USA is 191/250 on this list.
The entire human population spread over the whole land area of the world (excluding Antarctica) gives a population density of 57 people per km^2 compared to the USA's 33/km^2
The UK, which, (outside the major cities) is not particularly crowded has 272/km^2 for reference of what a built up country looks like.
The Netherlands, which is mostly Urban areas (and some tulip fields and windmills!) is at 411/km^2 (and doesn't feel that crowded, although admittedly they have the public transport and urban planning stuff mastered!)
What counts as "crowded" is admittedly subjective.
Note that the U.S. population density figure you cited factors in Alaska, which is a miserable place to live.
When I visited Britain, I thought it was overcrowded.