Ghani is making it clear, If Pakistan does not allow land access of Indian goods via Pakistan, He will stop land access of Pakistani goods to central Asia.
If Pakistani exports to central Asia are small, they will remain small..if Afghanistan closes land access central Asia.
Route through China(if and when developed) will be long cumbersome and uneconomical, Pakistan exports to Central Asia will not grow..rather shrink as they become uncompetetive.
"Profit not made is a loss" is Economics 101.
So is Pakistan willing to forego its profits, so that India does not make profit either..that is a question Pakistanis have to answer.
But then again by allowing India land access to Afghanistan, Pakistan stands loosing the Afghan market to Indian competition. Pakistan's export to Afghanistan >>> Pakistan's export to Central Asia. Not to forget Afghanistan depends heavily on Pakistan for all its imports. So India and Afghanistan have very little to bargain with here