The US rail system carries a lot more cargo than in Europe. On the order of 3 times more freight per mile of track. It is an also much cheaper to send freight by rail in the US compared to Europe. Reconfiguring the US rail system to even slightly more passenger friendly would seriously lower the amount of freight that can be transported by rail, as well as raising the price, and most of that would end up on trucks.
The other aspect is how the rail infrastructure is financed in the US vs Europe. In the US the infrastructure is to a large extent funded by the freight companies themselves, and in return their needs get priority. Take away that incentive and they'll stop funding the rail infrastructure meaning that much of that cost will end up pack on either the local or federal government, with all that that entails.
One of the heaviest rail, if not the heaviest rail in Europe, is a 500km combined freight and passenger rail that goes between Sweden and Norway (The Iron Ore Line). It alone carries more than the combined weight of all rail freight transportation in Norway, and close to 50% of all rail freight transportation in Sweden. It also happens to be one of the worlds oldest railways, built in 1888.
The biggest issue is speed. The maximum speed is just slightly above that of maximum highway speed, with freight speed limited to less than half of that.
That line is fantastic for freight (unless they've derailed an ore train again...), but the passenger service it offers would feel right at home in the US when it comes to both speed and number of departures. The passenger service to Norway leaves 0-2 times a day
The line between Kiruna and Narvik is so beautiful I’m not sure why you’d want it to go faster. The speed is heavily dictated by the number of tunnels and turns due to mountainous terrain. It couldn’t be much faster without very expensive kilometer long tunnels.
Population density in North Sweden and Norway is low enough that a few times a day is probably sufficient for most local travel. I haven’t been during peak tourist seasons when that number of trains might not be enough.
A fun fact is that since the ore trains travel mostly downhill, braking generates enough electricity that the ore empty trains can return to Kiruna effectively energy free.
We have the largest rail system of any country (USA 220k km vs EU 200k km). If you include the connections we use with Mexico and Canada it’s even larger. It’s almost all entirely freight. Trains can be 2000m long compared to 700m in the EU. It’s all built for freight.
2 km long trains are not long in the US anymore; in the west 3-4 km lengths are being seen more and more often. Turns out slower, longer trains filled with bulk commodities are better for business since they don't have tight delivery deadlines. There are towns where the train comes through for 45 minutes+.
Rail operators have also discovered a really nice side effect of ultra long trains: you don't have to pull into a siding to let a passenger train by as required by law if your train is longer than the siding.
Supposedly 10% of trains in the USA are about 10,000 feet or longer. Duckduckgo tells me that's about 3km. Supposedly there's at least one train 14,000 feet or longer.
It's worth noting that talking about the 'European' rail infrastructure is a bit of a misnomer since there is no standardisation of the rail system of regulations between countries and as such moving freight across multiple countries is basically never done.
Even for passenger transport the historical legacy of national rail networks means that travel across the continent hasn't been a priority. Recently EU initiatives seek to remedy this:
"the United States is the world's largest consumer market for a reason: its rivers. Transporting goods by water is 12 times cheaper than by land (which is why civilizations have always flourished around rivers). And the United States, Zeihan calculates, has more navigable waterways — 17,600 miles' worth — than the rest of the world. By comparison, he notes, China and Germany each have about 2,000 miles. And all of the Arab world has 120 miles."
To be fair, Germany is fairly small (by US/China) standards.
The continental US (no Alaska or Hawaii) is > 22.5 times as big as Germany but has only 8.8 times as many miles of "navigable waterways." (However, it's not clear if the US numbers include the Great Lakes or the oceans; LA to Seattle and Miami to NYC goes by ocean, not some river.)
But, that doesn't leave much for the rest of Europe.
The other aspect is how the rail infrastructure is financed in the US vs Europe. In the US the infrastructure is to a large extent funded by the freight companies themselves, and in return their needs get priority. Take away that incentive and they'll stop funding the rail infrastructure meaning that much of that cost will end up pack on either the local or federal government, with all that that entails.