The entire eastern seaboard from Boston down to Washington has a population of 50 million and a density of 900/sqm, 3 times the density of France, and 50% higher than Germany, and similar to Benelux (1000/sqm, 30 million)
The "America is big" argument doesn't really apply when you look at regions. Southern California is similar density to Italy and Switzerland.
You can't compare 'New Jersey' with the Netherlands (though, you could compared it to say the province of Utrecht) they are at different levels in the 'org' and that has massive effects for things like public transport. In order to get coast to coast public transport you'd have to take the whole of the country (the United States) into account and then you'll find that that average population density suddenly matters a lot.
Of course you can always chop up that big country into many small pieces and then focus on the few that are above the average of any other country but that's not a useful thing to do.
Sure, but coast-to-coast is not what matters. Moving people between where they need/want to go is what matters. I suppose a very large portion of all trips people in NJ makes on an annual basis is not coast-to-coast. It is within New Jersey or adjacent communities.
So even if you zoom out from let's say NL to all of Europe and you compare Europe with the United States you still end up with a difference in how public transport is arranged. There simply isn't a nearly empty heartland.
Compare public transport in the Berlin metro area (6 million, 500 per square mile) with the bay area (7 million, 1100 per square mile), or the Rhine-Main region (5 million, 1000 per square mile)
While the points you make are interesting, there is a massive swath of the us in between New York and LA, and I think that's where the argument is made.
I'm in Canada with 38 millions individuals in the second largest country in the world, I can assure you it's quite different from Europe. (Edit: just looked it up and we get about 15 people per mile!)
On average, North Americans also drive about double the distance europeans do per year.
95% of Canadians who drive on a commute in 2016 drove for under 1 hour, which can reasonably be approximated to under 50 miles [0]
If you remove the 3 territories the population of Canada doesn't change but the density pretty much doubles. 99.99% of Canadians have never even been to one of the territories. In the US, adding Alaska to the union made no difference to the viability of public transport, but massively reduced population density.
Looking at the density of a large country is meaningless. Just because Scotland has a population density the same as Michigan doesn't mean that the Central Belt can't maintain a decent public transport system. The density of that area of Scotland is around the Netherlands level.
What's important in the density of a specific economic area.
[0] https://www150.statcan.gc.ca/n1/pub/75-006-x/2019001/article...
You seem to take this to heart so I'll leave you to it.
Thank you for the correction.