If you ran high speed rail between the two most populated cities in the US (NYC and LA), it'd be a 14 hour journey. And there's not that many conveniently placed major cities along the way where it even makes sense to add more than a few stops.

I know we have a lot of rail enthusiasts here, but the average person tends not to like being stuck in a tube for 14 hours...even if that tube is substantially nicer and more roomy than an airplane.

Let's not even talk about the cost of constructing that route.