People keep saying economic factors dont matter, but having a comfortable home is key. It was the norm for most of human history; you could simply build one by yourself. It is probably still true in dirt-poor places with high-fertility rates. Family is conceptually proportional to a person's property and the tiny or temporary 21th century spaces just don't leave a lot of space for "let's have a kid"

(I think that 's the reason why the US has higher fertility that europe: bigger homes)