This is it- in the beginning, they used Islam with support from all over the country (never forget that, we have an extremism problem across the country, FATA just became the launching pad because of its proximity to Afghanistan, culture, geography, terrain but extremism is not a FATA only problem) , after APS /operations they became more ethno nats to the point I have seen some Pashtun nationalists bigging up their attacks on companies operating in FATA (despite knowing fully well that TTP single handily ended secular Pashtun nationalist movements, killed a lot of ethno nat intellectuals)
but at its core, its a criminal organization, I genuinely believe in that- they sell drugs, they do drugs, they extort businesses, target killings, kidnapping, ransom, gang war- its narco culture of latin america meeting islam and ethno nationalism