This is based on two factors:
The Land. KPK has more rugged terrain, where the water basin is often much deeper than the water basin in Sindh. This means that deep well construction in KPK takes more time and requires more specialized equipment to drill
The Supplies. Sindh houses the largest ports in Pakistan, making it not only easier, but also cheaper to get materials for building wells. Whereas in KPK, the material needed is often shipped from other areas in Pakistan, which contributes to an overall increase in cost of production.