If you compare Europe with developing countries a lot of people have comfortable incomes and even in the wealthiest countries birth rates are below replacement levels. You can keep coming with reasons like lack of healthcare, childcare, expensive homes and so on but the fact is that people in Africa don't have any of that and they still have more kids. Even in Europe or US people used to have more kids in way worse economic situation than today. The idea that people felt they have "comfortable income" to have 5 kids while working 6 days a week at a coal mine and living in a one bedroom apartment but can't have kids today because they can't put each one in separate room is just silly. People used to have a lot of kids because it was a necessity. Once the necessity was gone they stopped.
A lot of people want to form a family. They want to have a kid or two. Once they do they stop procreating because there's no natural drive to keep having more and more children. They keep having sex because there is natural drive for that but the drive to have kids is just something you made up.
There continue to be atomic bombs. Do people have natural drive to build them?