There are all sorts of alternative histories possibly, but in the one we live in people decided that they didn't need rail transit any more; autos were better. And they were, for quite a while, given construction of a fantastic road system. Buses were sufficient for those that were forced to ride it for lack of a car. Interestingly, much of that massively expanded road system is now 50-100 years old and falling apart for lack of maintenance and because of use by vehicles far heavier and more numerous than was ever expected; the road system, in the Bay Area and elsewhere, is facing its after-WW2 moment, with 20-50 years design lives well past in most places.

There was no political possibility in most places (SF a conspicuous exception with the Muni), for government ownership and/or operation of transit before the mid-late 1960s, and it didn't become more or less universal until the mid-late 1970s. Older rail transit was just worn out after WW2 (in many places even before the war) and needed work that wasn't justifiable for the private transit companies (or even most of the few remaining municipal rail lines) considering the cost and probable return; even buses only put off the inevitable for some of them. Did National City Lines push the process along a bit faster than might have happened otherwise? Conspiracy theory and limited evidence suggests that they did, but that was politically and socially acceptable (if not demanded) at the time and is done - the old rail systems are gone and the newer systems are government operations with all the inefficiency and occasional oddness that comes with that.

Question now is: how can we make things better for modern needs. Nostalgia for the old systems is fine as entertainment and documentation of history (there's certainly something to be learned from it), but should not be allowed to cloud what we're doing now - the old stuff was old and broken, and wouldn't have survived under private (NCL) ownership or government ownership of the 1950-60 era anyway. LA has been doing a pretty good job with their new rail lines, overall, but they've also been more successful than most at getting sales tax measures passed for the necessary funding, and while they do have a gaggle of smaller agencies 3 or 4 have been dominant for so long that things can be worked out for regional-scale projects. The Balkan nature of Bay Area transit seems to have placed BART in a de facto lead role because it crosses the walls between other transit jurisdictions. Whether that's good, bad, amusing, or infuriating depends more on the color and coverage of ones' tinfoil hat than anything intentional, and provides a little light entertainment for those of us who once lived there but no longer can.

Some of the current BART travails aren't so far off from what was happening after WW2 on the private lines - the bill is coming due for many years of limited (it costs money, and it's not glitzy/shiny like expansions) maintenance. In BART's case, it's happening in a system that has a lot of unique features driven by a desire in the beginning to just be completely different (Monte Python comment there) because for marketing (as well as engineering) reasons the old Key System concept just didn't work any more. The uniqueness certainly increases repair/maintenance cost. But the marketing worked: the demand now considerably exceeds the supply. Most of that is a result of simple growth in population and income, though, with travel needs that were deliberately (with political support) not met by those managing the road system. BART made the present-day Bay Area possible, just like the Key System did for a smaller area in Berkeley & Oakland. Give it credit for that, and now try to figure out how to pay for fixing it to last another 50 years.