Unless you think LA should go London/NYC style and build a load of stations, there is still the problem of what to do if you're not near a station at the start or end.
If it involves a bus connection, people will just drive
LA is already doing quite a lot in its transportation system. But just spending a bunch of money on a bunch of project isn't enough. They need to evolve into a higher level thinking about transportation. Currently its just 'money here for project X', 'money here for project Y'. And then they need to evolve again and think about the whole city in a new way. Transportation and land use planning a 100% linked, to have good transportation you need good land use planning. That requires reforms in zoning codes, building codes, parking regulation, road regulation and a number of other things.
In some sense US cities are actually well prepared, they have tons of space on their gigantic roads to have priority bus lanes, bike lanes and many other things like that. Road safety and transportation could be improved by a gigantic amount with simply changes in road design and investment patterns.
How to achieve that politically, well, I don't know.
There are other alternatives. Short commute by bicycle to main stations a la french/dutch style. Requires less investment for safe bike lanes but it pisses off car people.
Trams are also much cheaper than metro or train lines and serve metropolitan areas pretty well but they anger house owners and nobody wants to take public transit, thats poor people stuff.
It will take a lot of disillusion from cars before any decent alternative gets traction. Took long in Europe and is still ongoing for most of it, it will take even longer in the US.
People might be stubborn enough to only turn away from cars when the big traffic jams are all made of self driving electric cars with one or two people inside going all to the same places.
LA is literally filled to the fucking brim with parking lots, so many fucking parking lots. You have enough space for more stations then Paris.
And yet somehow in most large cities people use trams and bus in large numbers and don't 'just drive'. Crazy to consider that some people don't even have to own a car in such a city. If you have proper transportation infrastructure, those buses/trams can be faster then private car traffic.
Its called a 'transportation system' for a reason, walking, biking, buses, trams, trains all work together to provide something that practically moves millions of people a day even in the largest cities in the world.
Unless you think LA should go London/NYC style and build a load of stations, there is still the problem of what to do if you're not near a station at the start or end. If it involves a bus connection, people will just drive