Perhaps the HSR people are recognizing how difficult it's going to be to fight the NIMBYS and the exhorbitant cost of land acquisition if they choose to build an all-new dedicated route. The "easy" thing to do is use existing tracks and right-of-way. Land acquisition costs and NIMBY opposition are probably also the biggest reasons why the Vegas "bullet train" is proposed to originate / terminate somewhere near Victorville. Here is this country, you try and build new things only where people are scarce and they won't get too upset over the idea. That might also explains why the first starter project for HSR is the Borden-to-Corcoran "corridor". Who's going to complain about the noise and vibarations? Some cows, horses and sheep?

You can be assured that IF HSR ever arrives in California, it will be done WRONG. It's not about making sense. It'a ALL about placating politicians.