There tends to be a pro-growth attitude with city density even among environmentalists. I suppose they are somehow assuming more humans in one place means fewer humans everywhere else messing up nature. Of course, we need nature, nature needs us, and we are natural. The problem is we've been behaving rather unnaturally.
So it dawned on me the megacities of the world tend to us government power to accrue more power to itself, which in turn leads more people to go to the megacity. I think it was some discussion of Tokyo. Tokyo politicians appear to be dominating Japan.
But there are similar issues everywhere, and I realized city population density is likely very similar to economies of scale. In all likelihood, given the nature of government costs, businesses have become bigger because then they can distribute those costs across more transactions, whereas if there weren't all those costs, then there would be more small, local businesses.
A similar thing happens with cities. Then there is the political equivalent to stealing- cities tend to annex new areas in order to tax them. Naturally they tax them before they put in new infrastructure, so some politician can make his books look good by annexing and taxing while not (yet) providing services. The city's budget begins to look bad when they finally do get around to putting in infrastructure and providing services, but the temptation is to do it again. What is good or bad is determined by election cycle time, and there is no one with an ownership interest available to take the long view.