France’s new high-speed train design has Americans asking: Why can’t we have that?

Especially considering all of your major cities are in a straight line.

American here. We know exactly why we can't have this.

• No prior experience in building and operating high speed rail.
• Track standards must be much higher.
• Track must be completely secure from people and animals, and geology. This means high fences and shallow cuttings set far back from the running lines.
• The line can only be crossed by bridges or tunnels. No level crossings.
• Long distances pose issues in crew turnaround.
• Track must be as straight and flat as possible. North America has space, but also has geography.
• Reliable catenary power supply.

So it's an even better use case for high-speed rail, is what you're saying.

If you compare the US to Europe as a whole, there isn't a whole lot of difference. Europe also has many different countries with far more autonomy than US states, yet somehow they are all connected with a far better rail system than the US.

It's true, the U.S is too large for cars. Everyone needs to have their own personal airplane and use it for all trips since the country is so large, this is the only solution that can adequately serve all trips and hence must be the exclusive option