I've heard the theory floated that this is at least in part due to furious lobbying against it by taxi companies, who currently have a de facto monopoly on tran

I've heard the theory floated that this is at least in part due to furious lobbying against it by taxi companies, who currently have a de facto monopoly on transport at night. More likely it's just for train maintenance, and indeed, 24-hour train operation is vanishingly rare, with NYC and Chicago the only well-known major cities with it. Tokyo does stand out by not even having night buses though. (It used to have a skeletal network, but even that was killed off by COVID.)