Why is Cognizant not hiring Periyar University? Why are they looking for only graduation and not talent of the persons? Why dont they give opportunities?

Talent is not what companies seek, they wish to hire someone with average talent just to sell their products.

There is a training period given to someone who gets recruited as a fresher, and that costs money to the company and to recover that, they have a certain period of work assigned to the employee. Even though Cognizant doesn't have a bond, they have something similar. 

If you were extremely talented, you wouldn't want to work for a client where your task involves running a SQL query, or preparing reports or even fixing bugs or testing if on a page all buttons are working or not.

You will want to leave as soon as possible which they don't want. So they hire people with an average IQ, those who can do the required tasks when they want and don't argue much.