I think the reason is that children are a long-term project - 18-20 years at least. You might be living on a farm right now, but if you had an inkling that you

I think the reason is that children are a long-term project - 18-20 years at least. You might be living on a farm right now, but if you had an inkling that you will eventually move out to the city, you probably don't want to take on an expensive project - like having kids. Back in 1850s, if you were a farmer, you likely thought that you'll die a farmer. But today, if you're on a farm, you still get to see what's happening in the cities, often in real-time. And maybe you think that you'll eventually move there too, and skip having kids.