The old guard of the Taliban may still retain some loyalties to Pakistan - Mullah Omar, Hekmetyar, Haqqani etc - it is the new leadership that has sprung up that is more inline with Al Qaeda and has no loyalty to Pakistan, and sees it as supporting the US invasion of Afghanistan.
The Pakistani Taliban are from the Pakistan, so if the aim of the Afghan Taliban was to impose their version of Islam on all of Afghanistan, what do you think the aim of the Pakistani Taliban are?
Some Pakistani Taliban leaders, such as Gul Bahadur and Mullah Nazir, are operating primarily in support of the Afghan insurgency, driven by the perception of the US invasion and slaughter of Afghan Pashtun, and have little interest in expanding into Pakistan. These taliban leaders are the ones you typically hear referred to as 'pro-government' and 'good Taliban' in Pakistani circles.
Then of course there are the Al Qaeda affiliates and terrorist sectarian organizations such as the Lashkar-e-Jhangvi that also find haven in some of these areas, mostly in the territory where Baitullah and other TTP leaders hold sway.