Well, the reason the Pakistanis helped them get into power in the first place was so that the Afghans couldnt be used by the Indians. There is genuine and very really fear that India will try to surround Pak on both sides.
Another reason is that the Taliban were the only friendly govt ever to rule in Afghanistan. All others were constantly trying to undermine Pakistan by supporting Indians, and trying to start a Pashtun uprising in the Frontier.
If the Taliban came back, Pakistan would again have a buffer against Indians in the East. Also, the FATA situation would be resolved on its own.
Ofcourse, im not saying having Taliban back would be ideal in the long run, but it wouldnt be a disaster for PAK either.