[kaibee]

The land has gotten so expensive that the kind of people who can afford a SFH lot for their personal use, not to become a duplex or quadplex or whatever, can also afford to build a 2400 sqft house without it really mattering. Now a quadplex in the same spot could split that lot cost across 4 families.

[nemo44x]

Depends where you are. In most places land is quite cheap.

[dchftcs]

In places where land is cheap, infrastructure is expensive. Roads, electricity, water, sewers, internet. Higher commute cost is also a cost in productivity.

[YATA0]

This is often touted, but I just doubt that electricity, water, and sewers are more expensive outside of the city.

My father managed several factories in the LA area. Upgrading the electrical for new equipment in the close to downtown factory was going to cost something like a 6 to 7 figure sum. The factory in the boondocks upgrade was a quarter of the price.

[dchftcs]

Factories are themselves dense in resource usage, so it's different. It's a matter of scale.

A suburban neighborhood that hosts a few dozens of families requires more infrastructure, but can be replaced by a single 10 to 20-story building. An large apartment complex can serve hundreds of families.

Now, it doesn't have to be a dichotomy. It should be even more cost effective to build tall apartment buildings in the suburbs near the city. City-nations tend to expand capacity by creating new towns in suburban areas and extensive planning. That's much more efficient than US-style suburban sprawl.