There could be many reasons ranging from poverty where the girl child is traded with a much older man to settle the debts. In some cases marrying a young girl to an older man is considered good for the safety and security of the girl child.

Then there are wealthy families who in the name of family honor and at times based on associated morality issues (mainly virginity of the girl child being the issue) get there children in that arrangement at early age. At times even based on the current economic condition of the family so that in case the fortune changes the fate of the child (specially the girl child) is safeguarded.

There may be many others but the fact remains it is not right and all efforts need to be done to eradicate it completely as it is reported to severely affect such children at times even resulting in their death (specially the girl child).