Why did not Indira Gandhi after comprehensively winning a war, not leverage 93,000 Pak POWs to 1. Obtain POK in return? 2. Atleast change the Kashmi

Why did not Indira Gandhi after comprehensively winning a war, not leverage 93,000 Pak POWs to 1. Obtain POK in return? 2. Atleast change the Kashmi