Revealed preference. Usage of train travel (public transit in general) goes down with income, and people in the US have an order of magnitude more disposable income versus Russia.
The take rate of air conditioning in subsaharan Africa is far lower compared to similar-climate places like Florida, but I wouldn't use that fact to posit that sans-AC is somehow better.
People with other options don’t take the train in (most of) the USA because the trains in (most of) the USA are bad.
Of course the US is far larger than any single EU country, but the cities aren’t evenly distributed. There are many clusters of decently-close cities, and vast areas with very few large cities at all. Salt Lake or Denver may never have much useful intercity rail, but lots of regions could have it if we chose to build it (and learn from those who build it well, unlike California HSR).
The take rate of air conditioning in subsaharan Africa is far lower compared to similar-climate places like Florida, but I wouldn't use that fact to posit that sans-AC is somehow better.