According to this post by Harvard Business Review, it's because they don't have proper housing.
In a 2001 World Bank report, Voices of the Poor, those living in poverty identified better housing as a pressing priority. In recent decades, studies by the World Health Organization (WHO) affirmed what the poor have known all along: housing and health are intrinsically linked.
Yes, and you need a refrigerator to keep beer cold. But without electricity the refrigerator fails to provide what people in rich countries thought it would.
The same is true in the case of providing housing to poor in undeveloped countries. They're poor for a reason and it has nothing to do with housing. Housing is a byproduct of effective institutions like property rights. Without proper institutions, it doesn't matter how many homes you provide them. In fact, without effective property rights, any home that is provided as part of an aid program is likely to be co-opted to benefit some warlord to the detriment of the poor.
The plight of the poor will not be changed until their countries adopt institutional reform. If you want to change a poor outcome to a beneficial outcome, change the rules of the game.
