In an environment where people have more money everything gets more expensive, but labor does it more and faster. That’s Baumol’s cost disease. Only very expensive internationally traded capital goods and financial products have a single global price. Haircuts and coffee are more expensive in the US and Switzerland than in Ethiopia. The US does have unusually high construction costs, but that’s incompetence, see Alon Levy’s work. But food, clothes and many other things are cheaper than in other developed countries and the US is a technological leader in more or less everything, as in among the top 3 countries.
People who can’t save and borrow on bad terms exist everywhere. The US is different from Germany, but those people exist there too. The US is not different enough for a special explanation to be needed.
It's not really so much incompetence on the developers' part. The US has an overlapping patchwork of jurisdictions and regulatory authority at the federal, state, county/parish, city, and often other levels (township, flood control district, sometimes a converged health department...). The number of permits, regulations, inspections, and taxes on top of any project often costs as much as the materials and sometimes as much as the labor.
People who can’t save and borrow on bad terms exist everywhere. The US is different from Germany, but those people exist there too. The US is not different enough for a special explanation to be needed.