One is opportunity cost: You simply have more options (especially women), so having children now comes at the cost of many other potential paths whereas it used to be the default.
Housing costs: Most people want to live in a few cities per country and every desirable city I've ever heard of has an affordable housing crisis. When you can barely afford enough space for yourself, how are you going to have a room for a baby, let alone multiple.
Exactly. Traditionally, the man was supposed to be the breadwinner, women weren't expected to have a career, and what would she do all day at home after getting married? Of course she would get a lot of kids.
> Housing costs: Most people want to live in a few cities per country and every desirable city I've ever heard of has an affordable housing crisis. When you can barely afford enough space for yourself, how are you going to have a room for a baby, let alone multiple.
Not sure how strong this effect really is. I'm not aware available housing space having decreased over time.