Well can you blame the Pakistanis for not doing so???? So let's see. If the trade was opened up, thousands of trucks will go from India to Afghanistan and back. These trucks and their drivers will stop in different cities, and at stops when they need to. Who can guarantee that weapons supplies and money wouldn't be coming into Pakistan directly through RAW or even from the Afghan side??? Why would Pakistan risk their own national security and invite more bomb blasts and killings of their innocent citizens?
On the same note, Pakistan actually doesn't need to access Central Asia. The Chinese population in the region which Pakistan will be supporting through Gawader is over 350 million people. So its Pakistan (200 million people) + Pakstan and a half (350 million Chinese people along the trade corridor in Western China). So when Pakistani roads, ports, shipping, rail road, airways, etc, are providing for 2.5 times the original population of Pakistan, Pakistan will be VERY busy in accommodating such a big population and obviously, getting its economy to a whole new level super fast. She doesn't need to worry about the Central Asian part right now.
In the next 3-7 years, after Pakistan expands her infrastructure enough to support such a huge Chinese population through its trade route, it would already be in the top 20 economies. At that time, the Chinese would've built the trade routes to Russia and Pakistan can use those trade routes through China. There is a 0% chance that Afghanistan will get up and stare China down, to be frank here. Within the next 3-5 years, I think China will be cutting large infrastructure deals with Afghanistan too. I don't think Afghans want to lose millions of jobs and billions of trade with China by pissing off the Pakistanis. Till this trade boom starts with Afghanistan, Pakistan doesn't need to worry about it too much. She needs to keep expanding her economy and get into the top 20 line.