Sure, but the distances between cities in a huge country like the USA tend to be much greater than in Europe or Japan. Even if you had high speed rail it’d still take a very long time to cross the continent!
High speed trains do exist, or are being built, in more densely populated US regions (eg Northeast corridor, California).
The distances between cities in California or the upper East coast isn't. Both places have a high enough population density to support a good train network.
No one is suggesting that you take train from New York to LA but rather that you take a train from LA to San Francisco or Boston to New York. Similarly in Europe most people don't take a train from London to Rome but people will often take a train from London to Paris or Barcelona to Madrid. Any flight of 3 hours or less is usually faster and more comfortable as a train ride.
For those who don't know, people take trains between cities in the US Northeast Corridor all the time. In fact, that's pretty much Amtrak's only profitable region (money that it then loses in the rest of the country). And Amtrak actually has significant modernization plans in part because some routes are at capacity during busy times.
There would be even higher usage if Amtrak service in the region was actually good instead of just passable. The fastest service between New York and DC averages only 82 mph and it's even slower if you go past either of those cities. The allegedly "high-speed" service between New York and Boston averages only 66 mph. That's not even hitting the upper end of highway speeds.
There is very low population density between the LA and SF metro areas, which are roughly 350 miles apart (400 miles from city center to city center). This is one of the reasons that a HSR has been such a hard sell.
Big cities with nothing in-between is a good sell for HSR. Europe's two largest countries that have that population distribution pattern (France, Spain) rely heavily on very fast HSR (300-350km/h). The countries with more distributed, but also more dense population (UK, Germany) rely more on fast networks with more stops, but less maximum speed (200-250km/h).
It takes around 4-5 days to cross the US by train.
The problem is, the regular seats are shoulder to shoulder, there's no showers, and everyone shares a bathroom. Plus, they gouge you relentlessly with food rates.
It doesn't seem like it would be a fun experience at all due to those conditions (but would be fun otherwise).
Of course you could spend $1,000+ each way to get a "sleeper seat" which comes with a shower and meals but then it's like you're essentially paying $700 for a shower and a touch of privacy. It's just off putting to me based on principle.
High speed trains do exist, or are being built, in more densely populated US regions (eg Northeast corridor, California).