Dense infra is easier and cheaper to build and maintain than inherently sprawling single family infra where you lay down a lot of material and fixed costs just to service each single home and the infra between them.

The tax base you have per meter of sprawling single family infra doesn't even necessarily cover the maintenance. https://www.strongtowns.org/journal/2024/4/1/heres-the-real-...

And "build moar housing" trivially entails "and the infra to go with it". You're making the opposite mistake by assuming that the solution we already have is somehow better and more affordable only by the virtue that we currently have it which would only make sense if there was no maintenance needed.

You might enjoy the book Scale by Geoffrey West. One of the cool things he shows is that infrastructure needs of cities scale with an exponent of 0.85 while social things like incomes, patents but also crime scale with an exponent of 1.15. So as cities grow they get more efficient and it seems to be somewhat of a natural law that crosses countries and cultures.