That's not how it works. HSR could be used to alleviate traffic in dense urban regions, without actual cross-country interconnectedness.

So-Cal, Nor-Cal AND something connecting the two with a couple of stops in between.

Salt Lake area.

Houston - Forth-Worth-Dallas - Austin triangle.

Florida.

Urban areas connecting the Great Lakes.

I won't address the East Coast specifically, as it's quite evident that it'd have needed something around the same time Japan, Europe or China made strides.

Just to do a quick jump over the border, various governments have been attempting to build a HSR in the Windsor - Quebec City corridor for decades, but the political will is simply not there, and we still have the worlds widest and highest traffic highway that costs a fortune to maintain instead (along with the catastrophe that is the 407ETR).

Meanwhile as the latest example, Italy built up a new HSR system by 2015, in an area that is comparable in size and density to Florida. It has a monthly pass system that even allows you to take your bike on every route. It's also a national corporation. How come transit in NA is not allowed to be national, except when it comes to funding roads from tax payer money?