You are probably wrong that higher population densities *cause* lower fertility rates. Historically, cities were often population sinks due to higher disease rates, not low fertility. Diseases can increase death rates, but there's nothing about cities that causes lower fertility rates.
If density lowered fertility rates, then the Ashkenazi Jews would be basically extinct by now. Instead, the Jews had a huge population explosion in the 19th century, while mostly living in European cities. The Jewish population in Europe grew from about 2.5 million in 1800 to around 8.7 million by 1914, despite living primarily in urban areas. In many cases, the increasing Jewish population in cities lead to overcrowding in urban areas, hence one reason why antisemitism was rapidly growing.
Smaller apartment sizes aren't always the most profitable type of apartment for landlords and real estate developers to make. Smaller apartment sizes may be more favorable from a landlord's perspective, but that completely ignores the potential of the consumers to demand larger apartment sizes. If the demand is strong enough, then landlords will want to build larger apartment complexes, lest they lose out on a lot of potential profit.
You are probably wrong that higher population densities *cause* lower fertility rates. Historically, cities were often population sinks due to higher disease rates, not low fertility. Diseases can increase death rates, but there's nothing about cities that causes lower fertility rates.
If density lowered fertility rates, then the Ashkenazi Jews would be basically extinct by now. Instead, the Jews had a huge population explosion in the 19th century, while mostly living in European cities. The Jewish population in Europe grew from about 2.5 million in 1800 to around 8.7 million by 1914, despite living primarily in urban areas. In many cases, the increasing Jewish population in cities lead to overcrowding in urban areas, hence one reason why antisemitism was rapidly growing.
Smaller apartment sizes aren't always the most profitable type of apartment for landlords and real estate developers to make. Smaller apartment sizes may be more favorable from a landlord's perspective, but that completely ignores the potential of the consumers to demand larger apartment sizes. If the demand is strong enough, then landlords will want to build larger apartment complexes, lest they lose out on a lot of potential profit.
When I have time, I'll add a new section to my FAQs to address this topic in greater depth, since I surprisingly haven't covered it yet. https://zerocontradictions.net/faqs/overpopulation