> Why did people want to have them in the past

Most people are biologically wired to want children. "Survive and reproduce" is pretty much the driving motivation of all living things. Most children weren't conceived as a carefully planned retirement strategy. No cost/benefit calculation is required to convince most people to have children, but you can certainly force them into a position where they have to start thinking in those terms. We've just hit a point where societal and environmental factors are discouraging people from doing what they'd normally do.