you should check cost of highways in Moscow - $300M/mile. Hint - it isn't about terrain :)
Another factor at play is that TGV lines are purpose built for high-speed traffic (curve radius, climb rate, ...) while for example in Germany they are mostly shared. That makes the single TGV track cheaper, but you still ahve to built another track for lets say freight. If want another track, that is.
But the cool thing ist that TGV don't stop at every single village that happens to be the hometown of some polititian.
But the U.S. delegates decision-making to agencies and courts in a way that this doesn't happen. California might take input for a long time before deciding on its plan, but its final plan is still not final. Anyone can sue it for many different reasons. Maybe it violates the federal Clean Air Act, maybe it violates property rights, maybe something else. The decision is never final until every challenge to an agency or court is decided, which massively adds to uncertainty and costs.
Though it's somewhat difficult to separate out the 42km of new tunnels (expensive) and a whole bunch of new stations (expensive) including a whole bunch of revamped ones in the centre of London (very expensive).
$6.4 trillion in total government expenditures.
Largest welfare and entitlement programs.
Nearly 15% U6 unemployment. Collapsing labor force. Falling real incomes. 15% on food stamps. Massive fiscal mismanagement in every respect. Endless QE just to fund the government. 0% interest rates just to reach 1% GDP growth. Healthcare is clearly moving toward a completely socialized approach over time and completely away from any free market solution. Taxes are extremely high, between federal and state; typically higher than supposedly socialist European countries. America also has more economic regulations on the books than any other country (and that's rapidly expanding). The largest land owner in America is the government, by a drastic margin. Half of all mortgages are held by the government. And on and on.
Doesn't get any more old European Socialist than what America is today. It would be fiscally impossible to go any further.
We'll try.