The A in Pakistan stands for Afghanistan and dates to at least 1933. When the British were quitting India in 1947 and Pakistan was forming, why didn't the Afghani's join with Pakistan. Afghani's readily supported Pakistan's interests in Kashmir and shared at least some culture. As far as I can tell, little to no effort was taken to roll any of Afghanistan into Pakistan. Why didn't the A in the vision of Pakistan not materialize?
Because Afghanistan had already been a fully independent country for 30 years, the population of which was no more interested in the being subject to the hegemony of Choudhary Rahmat Ali's Punjabi imperialism than were the Bengalis. The latter unfortunately had to wait a quarter century to gain independence.
Ali's clever coining of an acronym in 1933, from the existing Urdu and Persian word for "Land of (the) Spiritually Pure", no more gives Pakistan right to claim governance of Afghanistan than James Madison's expansionist policy gave the U.S.A. sovereignty over Canada in 1812.
Governments are instituted among Men, deriving their just powers from the consent of the governed,
Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes. - U.S. Declaration of Independence