Even a train that drops you off in the middle of Los Angeles could leave you many hours from the actual place in Los Angeles you want to be.
This argument ignores the new and existing population clusters that form and grow along a transportation link. You only have to look at interstate highway system and how new population clusters formed and existing clusters grew along the links once interstate hwy were built. Just reviewing the I-35, I-10 in Texas will show you that. Same can be seen with local subways and light rails systems. The clusters near stations grow faster than rest of the city.
Also, when people in the US say "high speed rail", they usually seem to mean 180mph. That does not qualify as high speed rail overseas.
Upgrading the current low speed system to medium speed 180mph rail would mean that taking the train would actually be faster than driving (and for short air routes, faster than airport+flying).
My guess is that many existing routes would then become financially viable.
[1]: typical example -- https://en.wikipedia.org/wiki/Horseshoe_Curve_(Pennsylvania)
[2]: For a detailed example of what's possible & what isn't with existing corridors, you can look at this independent engineer's study of how to upgrade a rail route through Northern California: http://zierke.com/shasta_route/
You mean "start a gold rush".