As in the world history 9/11 plays a very important role, and it is openly known to the world that the mastermind of 9/11, Osama Bin Laden was well living under the protection of Pakistan's army. Most of the small or big time acts of terrorism in USA link to Pakistan.
Sharing the similar pain, we Indians are also badly affected by the terrorism emanating from Pakistan, and there are various evidences such as the recent Uri attack on Indian Army, where the state of Pakistan was helping the terrorists. In the Surgical Strike by India on the terrorist camps in Pakistan, 5 Pakistani army personnel were killed as the Pakistani army shelters these terrorist.
Hence, it is in the interest of USA and India, and the world that Pakistan be declared a terrorist country.