a compound reason.. Americans dont see it fit that Pakistan's airborne capability gets a massive boost helping it in rapid deployment in COIN operations or in a traditional war theatre.
On a lighter note, the Obama administration would have less chance to repeat their favourite rhetoric of “do more” if Pakistan uses them to rapidly deploys troops blocking the possible entry/ exit routes of terrorists.
Secondly such sale also doesn’t suit our eastern neighbour which happens to be a bigger and strategic partner of USA.. So it is purely business nothing personal
For whatever reason or conditions American policy makers have agreed to approve some military related sale, these chinooks don’t fit in and are way too good for us. Looking at the diplomats shooting issue recently, one can see the futility of our “strategic friendship” with the USA where it is threatening with cutting off the military assistance and opening up the AQ Khan’s nuclear issue and all other issues that are normally played out by countries hostile towards Pakistan.
So we can watch but cant touch like myself when I saw this beast perform in Farnbough last year. It is very graceful and agile machine with some jaw dropping manoeuvres.