The reason mass transit works in Manhattan is that you can have a subway train arrive every five minutes and still have it full of people. The reason you can do that is that Manhattan has more than 25 times the population density of LA County.

To fill the same subway cars in LA would require intervals more than 25 times longer, i.e. more than two hours instead of every five minutes, and then it's garbage and nobody wants to use it. Or, in practice, you only run mass transit along the most popular routes and then the majority of people can't use it because it doesn't go where they're going.

Making it less convenient to drive doesn't really fix that, all it does is make more people miserable, because you make driving worse where no viable alternative to driving is available. The only real way to fix it is to reduce sprawl so that you have more density over less area -- and that's only possible in the long-term, so in the short-term LA is pretty screwed for traffic. But that's no excuse to not be working on the long-term solution.