Actually, the fault is not of the Afghans -- it is that of Pakistan -- Does or Do Pakistanis actually see a border when they regard the Durand line?? If your answer is yes, then reasonable people can say "Show me" - What has Pakistan done to ASSERT and ENSURE the line is treated as a border?? Allowing multiple entry points in which documentation is anathema? Not Developing proper economic relations (customs union) to ensure that Afghans and Pakistanis do not have to suffer the ills of smuggling??.
Afghanistan is a battered and worn out country, it was never a well to do country - and truth be told, it's economy is actually a part of the economy of Pakistan -- This need not be a negative, and indeed turning this into a positive will completely change the security situation between Pakistan and Afghanistan -- but for that to happen, you will need a security apparatus that sees the national security and national interests of Pakistan in very broad ,complex terms.