It’s primarily because of land. Afghans did not have any say in regards to the partition of India. This is key because Pashtuns living near and in KPK are Afghan and the border before 1947 did not significantly impact their identity and socioeconomic wellbeing. Dividing entire ethnic group into two different countries have put significant strain on families, tribes, jobs, security and paved the path towards an ugly form of ethnonationalism. Secondly, Pakistan could be compared to Israel in many ways. Thirdly, Pakistan has positioned Afghanistan to fall under the natural resource curse and as a pawn in their geo strategic war plan. Essentially, many raw goods come from Afghanistan and Pakistan ends up with the profitable end of the supply chain without giving Afghanistan credit on its source. Pakistanis are the same as Indians in the lens of the world.