If the supply route is not that important as per what u are saying, then kindly ask US not to waste your tax dollars in sending delegations and generals asking for opening of the route, till these delegations and generals keep coming and ask for reopening the route, it negates what you just said above. They may have stocks for 6 months, other routes and aerial route might be open, but the economic value of the land route through pakistan is something which you are not getting. Do the math, may be you get the point of why the are sending delegations requesting to open the route.
And its not about a border post, when you need to take out your desperation and frustration, you kill to satisfy or reduce the desperation and frustration. We saw that in Iraq with US soldiers killing and raping, we saw recently the US soldier killing dozens of Afghans in their homes. many more examples, saw such actions in Vietnam also. Thus cold blooded murder of sleeping soldiers was to take out that frustration and desperation.