Hi Veena,
Usually, companies keep some of the workers on the payrolls of third parties to reduce the costs incurred by the company. If the worker is on the payroll of the company, they will be eligible for all the welfare activities that the company provides, which in turn will cost the company. They can even pay a lesser amount in terms of salaries to the workers if they are on the payrolls of third parties. Outsourcing the workers is a great advantage to the company. Usually, companies make a worker permanent if they do great work, and this permanent employment would encourage them to stay with the company for a longer period.
Regards,
Gowtam