It's the rate that women are getting pregnant. Circumstances and societal conditions can certainly curtail and slow the willingness of otherwise capable women to have families.
Chicken and egg problem. Cars are necessary because businesses/places to work are far apart, but they got to be the distance they were because cars are around. The US is a huge place, there was plenty of space to go around and the current situation is what follows from it.
English being a mess may be one of its charm points. Many languages in a trenchcoat, full of flavor and exceptions to its own rules and a headache to learn.