Why does the Kafeel keep the original passport of migrant?

The rule is that the Kafeel cannot confiscate or keep the original passport of the migrant. This is against international law and the standard employment contract. Most often than not, however, the Kafeel keeps it to secure that the migrant will not escape, run away or cease the contract because he or she does not have his or her travel documents. This would limit his or her movements and options.
In some countries, Kafeel keeps the passport to ensure that the migrant continues to work and be able to pay for his/her loan with the employer or the expenses incurred during the recruitment.