[davidw]

Compared to the same amount of services further spread out, infill is far cheaper, and tends to generate a lot more tax revenue compared to the infrastructure needs. Here's a sort of simplified, but real-world example that uses snow clearing:

https://bendyimby.com/2021/03/24/snow-and-financial-producti...

Something like sewers are more complicated, but the basic equation is that you're adding things in an area that's already served by infrastructure and often pretty good infrastructure at that, rather than adding in kilometers of brand new infrastructure for relatively low-revenue uses.

[sandworm101]

>> adding things in an area that's already served by infrastructure

Unlike in video games, "adding" load to infrastructure can cost more than running new lines. Everything from pipes to power lines have finite capacities. If a city sewer system is at capacity, as many are, dropping some more people into the middle (replacing a parking lot with houses) will require possibly ripping up the old sewer/water/power lines to expand them. And expanding their up/downstream connections. That can impact far far more than the local connection, often costing much more than green-field development. Imaging how much cost to open up and expand a sewer under any Manhattan street. Compare that to digging a trench through a green field out on the outskirts of town.

[ProfessorLayton]

Everything from pipes to power lines also have a finite lifespan, and many cities are succumbing to crumbling infrastructure as the low density suburban tax base isn't covering their costs, and is unsustainable in the long term.

Yes it costs a lot in absolute terms to rip up and expand a sewer lines in Manhattan, but that doesn't mean it costs more per person being served by that infrastructure.

[treis]

Snow removal is cheap. The expensive things like schools, criminal justice, and health care are all more expensive per person in denser cities.

[AnthonyMouse]

They're more expensive per person in cities with a higher cost of living, which often correlates with density. But zoning restrictions increase the cost of living by contributing to housing scarcity.

Density isn't the cause of high cost, it's the response to it. It's the market increasing supply in the presence of high demand. When prices are high you want more of it, not less.