I agree with you, but infrastructure is often built to expand future regions. Before the Golden Gate and Bay Bridges, there was a lot less commuting to SF. They only had ferries. Building the bridges allowed the broader region to expand and prosper.
If you (read NIMBYs) shut down all public policy designed to turn your sleepy town into a thriving one then it's just a self fulfilling prophecy.
This is a pretty common kind of blindspot for people to have, talking about how crazy it is to build transit to places with or lower populations or less population density, but forget that a lot of well-connected, dense places with good transit weren't very dense before good transit was built!
There is a reason these cities never got developed more than they are. It's kind of flat, unappealing scenery and it's boiling hot in the summer. People would rather live in LA. California has huge swathes of land with very, very low population density because nobody wants to live there.
Several decades ago, you could have levied the same criticisms against South San Jose, Morgan Hill, and so on. But people now want to live here.
There are basically two ways to sustain the growth in California. One is to greatly densify places like the SF Bay Area, another is to improve the infrastructure elsewhere. And I don't expect see residential high rises in Palo Alto any time soon.
Up north, there's plenty of places that are more desirable in terms of weather, but they're not gonna get developed for environmental reasons. So what's left?