California has the second highest total lane miles by state[0] and it has the highest number of registered vehicles of any state, by a big margin.[1]

Being a such a populous big state with only tiny, regional public transportation systems means everyone and their cousin drives everywhere, all the time. That's how.

[0]https://blog.cubitplanning.com/2010/02/road-miles-by-state/

[1]https://www.bts.gov/browse-statistical-products-and-data/sta...

I've lived in California for 30+ years now and what I've observed is that we spend huge amounts of money on infrastructure and a lot of the spend seems to be absolute waste. For example, there is no realistic reason for high speed rail to cost what it does per mile; I am certain that a very close inspection of the process would uncover huge amounts of waste, padding, and theft. On top of that, people have been able to limit development using enivronmental rules and other legal methods to slow down things that are truly needed.

I'm sure somebody has written a book already about how ostensibly wealthy societies can fail at basic infrastructure that they previously mastered, driven by greed and complacency and other socioeconomic factors. I think this has happened over and over again (Rome, and many other societies).