Just look at the physics of the problem. If I am going to be in an aluminum tube hurtling along at hundreds of miles an hour, do I want that aluminum tube to be five miles up in the air, where there is nothing to hit, or down at ground level, where there are all sorts of things to hit?
High speed rail might make sense for trips that are too short for aircraft, maybe up to 200 miles or so. For anything longer, there are better, cheaper, safer, less polluting and more comfortable alternatives.
It might make sense from San Diego to Los Angeles and from Sacramento to San Franciso.
A limited high speed rail system could be built very cheaply.
But unfortunately that only underscores why the rest of it isn’t really necessary and the politicians won’t hear it.