I remember reading a study that said this was not caused by poverty, at least not alone. It's also cultural. There are poorer areas in the world where they don't "burn to clear fields, cook stove with wood and burn cow dung" and also open defecation. At least that's what the study said, and that people doing these weren't all particularly poor. It would require a huge cultural shift and change of habits. Something that is really hard to do unfortunately.