Well US did realize all about Pakistan and they know it more than India. But they don't have any option, when it comes to fight with Afghanistan/Taliban. Geographically Afghanistan surrounded by Uzbekistan, Turkmenistan, Tajikistan (All part of previous USSR, which are not friendly to US) ,Iran (We all know how friendly are they with US) and Pakistan. So their best option is to bear Pakistan's nonsense while they can fight with Taliban.
