Let's be real here, it's because it doesn't matter. I'm going to get downvoted for that, but it's true, it doesn't matter on any level what world your children inherit when deciding to have them. Biologically it only matters you have them.
People still had children during the Chinese famine.
People still had children during the Siege of Leningrad.
People still had children during the black death.
I feel like this subreddit greatly underestimates how driven people are to have children no mater what. It's quite literally what our bodies are designed to do.
Denying the programming is the exception and legitimately a difficult thing to do. Don't think just because this is a community of people who have managed to do it that it's common.