both India and Pakistan are relatively new countries in that there less then 80 years old
the region that is Pakistan and parts of Northern India heave been the crossroads of ancient trade, the influence ranges from Persian/Indo-Aryan/Afghan/Steppe Nomadt's also worth pointing out that a huge proportion of Pakistanis aren't historically from Pakistan. Before the British showed up, the areas that are now India and Pakistan were a huge patchwork of separate kingdoms and fiefdoms, and you'd have Hindu and Muslim (and some others, notably Sikh) kingdoms side by side all the way up and down the subcontinent. When the britbongs showed up and "colonized" the place they decided to lump it all together into one country called India. After independence there was major violence between Hindu and Muslim populations, and it was eventually decided to split India into two countries, the ones that are now India and Pakistan, and when that happened Muslims from all over what's now India moved to Pakistan, and vice versa for Hindus that were in what's now Pakistan. There are also a lot of Pakistanis from other "stans" in Central Asia.
So tl;dr Pakistanis are very diverse looking because they come from all over the whole Indian subcontinent,Persia and Central Asia, not just from modern Pakistan itself.