The first distro I used was Ubuntu as part of a computer class at school, but it was preinstalled on a school computer. The first distro I installed on a personal computer was Arch because le reddit said it was le epic hackerman’s IMPOSSIBLE CHALLENGE TO INSTALL distro. It installed, and after that I didn’t use it because my favorite Windows apps couldn’t work.
No, it’s 100% economics. Why do you think that having “careers, lives and travel” (as if having a family is not having a life?) is more appealing to modern first worlders? Because it doesn’t impact their finances severely. Having more children in impoverished countries is a financial gain because children are free labor and lottery tickets to get the entire family out of poverty. In wealthy countries, children are only a financial loss.