If I had to take my guess, a mixture of corruption and apathy. The big effort at trustbusting and dealing with the railroad tycoons back at the tail end of the 19th century was the last time this country really made a substantial effort to stop powerful companies and the super-rich individuals controlling them from fucking the people. These days we're ignoring our legislature passing laws which make it easier for corporations and the rich to buy themselves more power. It's a rather depressing feedback loop. Within the current paradigm I'd not be surprised if it's outright impossible to effect real change at this point, since we're seeing the same gorram behavior from the pharmaceutical and insurance industries, among others.
The sad thing is that it's that exact sense of inability to create real change that fosters the exact apathy that puts it into place.
Though we did manage to finally break the DeBeers cartel hold on the diamond market a few years back, so that's a good thing for anti-monopoly stuff.
@On California Public Transport
Another aspect that limit's California's ability for public transport is the fact that many of it's cities were constructed both after the invent of the automobile
and expanded greatly during the "suburban craze" of people trying to move out of the cities (but still be close enough to work there). The result is a very decentralized design in most of their cities, that wrecks their ability to set up public transport (L.A. is a particularly good example of
bad places for public transport, though it's certainly getting better). While this has much more of an effect on in-city public transport, it does have negative effects on intercity transport, after all, if there is no solid city center in many cities then where are you supposed to connect your train line to? And if a city doesn't have any good in-city public transportation then how are people supposed to get around the city they just caught the train into? If you are going to need to rent a car once you get to your destination anyways it lowers public transport uses by quite a bit, and then it gets caught in the vicious cycle of "people aren't using our public transport (because it sucks) so we aren't going to invest more money into it to make it better, so it still sucks and people aren't going to use it, and ...".
If anything I'd be more willing to place the blame on the city planners and public atmosphere when many of its cities were planned and expanded than on some sort of automobile conspiracy (which did influence public opinion somewhat, I'd guess
).