Either their country as a whole is disadvantaged, or just their family. These conditions are very appealing to businesses. These businesses think that they can get cheap labor, and they are usually correct. Any business person could tell you that the cheaper something is to make, the bigger profit one can get. This leads some companies to exploit children.
Children are at that stage in life where they are suppose to be protected.
They are suppose to be told what to do and are not capable of doing too much thinking for themselves. They are the hapless victims of big business and greed. Since children are at such a tender stage in their development they are very easy to control and they are also very helpless. Because of this helplessness, it is easy to extract work from them cheaply. This is the same reason that slave labor persisted in American history.