Raz if you look at the tenets of Deobandi they are heavily influenced by Wahhabi school of thought.
Deobandi - Wikipedia, the free encyclopedia
Beliefs
Deobandi beliefs, like those of other Muslims, are based on the Quran and Sunnah. They follow any one of the four; Imam Abu Hanifa, Imam Shafi, Imam Malik, and Imam Ahmad bin Hanbal,but they primarily follow Hanafi school of fiqh.[13] and follow the Ash'ari and Maturidi schools of Aqidah.[14] In Sufism they follow Chishti, Naqshbandi, Suhrawardi and Qadri Sufi orders.[15][16][17]
The Deobandi movement is known for its harsh stance against many practices common in the Indian subcontinent such as building over tombs, celebrating Milad al-Nabi, and calling on the prophets and saints for assistance. The founders of the Deobandi movement
were influenced by the Wahhabi movement.[18]
Global encyclopedia of Islamic Mystics and Mysticism, page 62
You want another source yaar? I got you right now.
Deobandi Islam
Although the majority of the Islamic population (Sunni) in Afghanistan and Pakistan, belong to the Hanafi sect, the theologians who have pushed Pakistan towards Islamic Radicalism for decades, as well as the ones who were the founders of the Taliban, espoused Wahabi rhetoric and ideals. This sect took its inspiration from Saudi Hanbali theologians who immigrated there in the 18th century, to help their Indian Muslim brothers with Hanbali theological inspiration against the British colonialists. Propelled by oil-generated wealth, the Wahhabi worldview increasingly co-opted the Deobandi movement in South Asia.
Hanafi was the dominant group of Muslims in South Asia. The leaders of Hanafi sect were known as Pirs or Saints and were Sufis believing in spirituality and such.
Deobandi is a part of the Hanbali sect which is prevalent in the Arabian Peninsula which is basically Salafi/ Wahhabi.
Sorry for getting off topic.
The question is why weren't Deobandis so militant if they have been here since the 18th century and why are they so militant now. The answer to that is simple, today they have both oil money and the weapons to back them up so they have made their demands more well known.
That being said my grandmother is Wahabbi although my forefathers were Sufi Pirs so I am in no way trying to say all Wahabbis/ Salafis are militant. The majority of militants however find their reasoning to justify their crimes in Wahhabi/Salafi/Deobandi texts and we must confront these teachings if we want to know why Pakistan has so much widespread chaos today.