I have for years been studying the Afghan psyche, why the country is the way it is. Why it behaves with Pakistan the way it does, why even the so called Pakistani proxy government of the Taliban didn't accept the border between Afghanistan and Pakistan.
All of this has led me to the conclusion, that at its core, basic Afghan nationalism (not even far right) states that the western half of Pakistan belongs to them and they will never stop till they get it. They see Pakistani presence in that region as the presence of a colonial outsider. The fact that Pakistan is many times stronger than them has forced them into an uneasy de facto recognition of the border temporarily, but the day Pakistan is weak enough for them to carve it up, they will immideately join the party.
Now I am not an individual who calls for hostilities with other nations unnecessarily. Heck even Germany (Prussia) and France, two countries at each others throat for centuries are best friends today. What was required however for this to happen was for Germany to accept that Alsace Lorraine belongs to France and that the existing border between the two countries was legitimate. Once this acceptance came, peace, trade and development followed.
Similarly the day Afghanistan as a nation accepts that KPK and Balochistan are Pakistani territory, they will find no better friend in the region than Pakistan. However trying to befriend Afghanistan till this change happens is like France and Britain trying to appease German nationalists prior to WW2. You can try all the appeasement you want, build as many motorways, hand over Pakistani border check posts to the Afghan army, or send cricket teams to visit them, they will just see these concessions as small victories in their larger game of one day trying to take over all Pakhtun and Balochi inhabited territories.
PS: this idea of just the Kabul government being hostile to Pakistan, and the masses somehow being pro Pakistan, that many Pakistanis have been led into believing is bullocks. I personally have been to an Afghan mosque in the UK, where part of the jummah prayer dua was to denounce Pakistan, so closely have they intertwined religion and their nationalism. Such people cannot be rationalised with. I know many other people with similar experiences. At university I got into a real argument with an Afghan guy who was telling guillible white people in a UN society event that Pakistan was occupying half of Afghanistan, and massacring the oppressed peoples of these regions.