If Pathans, Punjabis, Balochis, Kashmiris, Sindhis could, why couldn't you. It was just meant to be the lingua franca of the nation, like Hindi is in India. Everyone is free to speak their mother tongue at home, with friends, cultivate it- no one's stopping you. And your Pakistan was formed on the basis of Muslim nationalism, where Islam is given first priority and jahilliya to be kept away from Muslims. AFAIK, Muslims are urged to leave Jahilliya as much as possible
Bengali was the least Islamic of the languages of then Pakistan and even your script wasn't nastaliq, so of course it didn't make sense why you guys still stuck to that jahil culture instead of adopting Urdu which was the carrier of Islamic culture of the subcontinent. Heck your Bengali Muslim women even wore bindis during those language agitations to assert "Bengali identity" lol. Where was "Muslim identity" then. You guys were visibly more concerned about Bengali language than getting Islamized through Urdu. So again I really don't know what you guys' primary identity is, Muslim or Bengali? Again, sanu ki