Because that extracting (pumping) facilities is not being expanded as per the increasing requirments. The Govt. focusing on the gas imports to earn more from the users as then it will be available to public near to double the international market prices.
There is a limit of well head and distributin line pressures for which transmission network needs expansion.
Another factor is the damage to the gas transmission system is the terrorist attacks on such facilities specially in Baluchistan (Though they are less frequent these days)