So you design a small condo, where still you can't evolve, because it's extremely hard to reach and agreement to rebuild at a certain point in future, you put something in common, something much more costly than individuals machines, who need external services for anything, with much more stringent norms (let's just say common laundry machines requirement for high temperature wash for sanitary reasons, while individuals one do not), still being unable to implement the new deal without making new buildings for what? To spare a little bit in capex significantly enlarging the opex? No thanks.

I do not have studies to cite because there are none on that subject both pro and against urban, only PRs stating that's certain something not giving any reproducible proof and it's extremely complex to measure real costs because we should build real similar communities living a significant amount of time to compare, it's not just an initial bill of materials comparison but a whole different economic model.

What I can say is that in EU some countries have most people in single family homes, some others the opposite, some very dense, like the Nederland 425.4 humans/km² with 81.3% in homes, still being a significant producer of meat and cheese, Belgium 381.79 humans/km² and 77.6% in homes, France 117.52 humans/km² and 62% in homes, Ireland 71.47 humans/km² and 89.4% while on the other side Italy with 200 humans/km² and 42.9% in homes, Spain with only 34.3% in homes that's to say except few very small, very populated countries there is room for both model, it's not a matter of density nor of mean richness, nor of industrial vs something else development and so on, it's a choice. This variety is not technically a proof but it's enough to say that both models are perfectly possible and mean Gini index, mean happiness level, financial stability and so on suggest that being less dense pay back better.

I'm European I do not know much about the real USA situation but I have been in the USA some times and... Did you see SF recently? All "the city" essentially in a decadent state, all "wealthy" spread around, mostly in single family homes, some in very small condos who honestly seems to have no reasons to exists seen their prices compared to those of the homes and the relative opex and resale value. NY? I've just seen a very small part of NY, but that's enough to say "I have no damn reason to be here". Of course I know USA suburbs failure but that's not due to the density or the fact they are made of single family homes, that's due to the fact they are built to IMPOSE commuting for the sake of automotive industry. They are residential ONLY. Here (France Alps behind the Riviera) anything is "a suburb" since there is no big city and actually no city at all but anything is intermixed. I'm in a residential are, but a 3km (1.9 miles) I have a supermarket, about the same distance a golf, a blacksmith and a window installer main office and few shops all being single family homes scattered around and small sheds or little buildings. This is essentially the "strong town" real world modern model, their own was the old far west model, witch was working indeed, but was a spread one of small villages dispersed in nature.