Possibly because the parents parents didn't value education and by the time the parents came to value education they were already stuck in the cycle of poverty.
If you took the vast majority of babies and had be adopt them (this is of course kid napping which I wouldn't agree to) they would grow up to be more successful than if they remain with their parents. Of course successful is in the eye of the judge, some of their parents in 40 years would be glad for my help and some would think their baby would be better off with them.
The above applies to most of the people reading this as well. (a few of you have admitted you don't want kids because you would be a bad parent, and a few more could be good parents to your own kids but bad for adopted kids - but overall these groups are a minority)