we did build a massive, efficient train system: for freight trains. We also have a Massive system for moving people: interstate highways. Those decisions were made years and years ago. Introducing a third system is hard to justify outside of highly obvious congested corridors like the Northeast

Existing rail is owned by the various freight transit companies. Those companies have absolutely zero desire to improve the infrastructure as high speed rail requires modifications that does not benefit freight rail. Then there’s the problem of land ownership, good luck getting the necessary route at a decent price (and governments won’t eminent domain property for rail anymore because of Eisenhower’s highway system). The last reason is why Acela only averages about 8mph faster than a regular train. In the NE corridor, the existing route is so windy that the Acela cannot really hit its max speeds. There is a short area where the Acela travels above 90mph, which I believe is between Delaware and DC. Once you get to NJ you are sharing tracks with various commuter lines which further adds congestion. Places like Texas and California it makes sense but the Northeast is a quagmire of epic proportions

You might find "Why America can't build" interesting, posted here a couple of days ago. There were a lot of comments discussing that question:

https://news.ycombinator.com/item?id=31890048