Most parents want their children to live a good life, whether they're from poor country or not. Besides, people used to have more sex in the past when life seemed much more hopeless than it is now. Granted, condoms didn't exist but these days, people aren't even dating anyway.
> The reasons have been written in this thread
It's all speculation at this point. If we knew the reasons, we'd solve the problem. Like the meaning of life, there are some things we can't know.