Then why do cities built around cars - that never had trains - still have central business districts? i.e. the entire south & west of the US, pretty much.
To get the same concentration-of-offices effects in new developments, like I mentioned. But take a look at the size of those central business districts compared to older cities; look at the population of LA vs Chicago or Boston vs the size of their downtowns. (And LA is one that did have some streetcars for a while - Phoenix would be an even more extreme example of a big metro area with a truly pretty small central business district.) There was a lot less pull outside of certain industries - new industries like tech largely avoided ever going downtown much in the first place, preferring big suburban office parks.
So if you don't even need the suburban office parks anymore, do things sprawl out even more in places like Austin or Dallas that are surrounded by empty land (vs somewhere like the Bay Area which is hitting geographical barriers)?
You end up with city/county hall, local courts, then the lawyers, general contractors, banks etc all clustering around that. There's a natural clustering of resources that happens just from local government. It's not uncommon for the largest hospitals in the region to be near city hall. From there it just snowballs.
That said, I'm not sure why the neighborhood around San Jose's City Hall is so dead, it's very odd experience to go there
So if you don't even need the suburban office parks anymore, do things sprawl out even more in places like Austin or Dallas that are surrounded by empty land (vs somewhere like the Bay Area which is hitting geographical barriers)?