There is no other explanation, similar to our non secure Southern border.
If the US really wanted to close the border, it might take all of a week or two to do so, and if the Pakis really wanted to end the problems in the territories they would do so, unless someone here is stating that this nuclear power is so feckless that they cannot sweep aside a few thousand tribesmen with AK47s.
If that is the reality, then India certainly has little to worry about with them.
And then, perhaps we should go in and take care of business.