50 years ago during the Cold War the economic trajectory of the two wasn’t so different, and pakistan also included what would become Bangladesh. Nixon was opening relations with China after the sino Soviet split, and India probably wouldn’t agree to ally with someone who was in the process of economically integrating with a country that they were actively fighting a border war with (sino Indian border war 1962-present). Pre Iranian revolution Iran was also a major ally and shares a significant land border with Pakistan, and probably most importantly, Pakistan was an ideal country to serve as a funnel for military assistance to the mujahideen to help fight the Soviet Union in Afghanistan, which would arguably lead to the economic drain and political quagmire that was a primary factor in its collapse.

Of course the mujahideen would then evolve to become Al Qaeda which Pakistan would harbor, Iran would have its revolution, Bangladesh would gain independence, and the Pakistani military dictatorship would squander the potential of their country on a nuclear program and trying to maintain an army of equal strength to a country 10x their population. But the choice had a lot more geopolitical merit way back then, and once it had been made it is not so easy as forgive and forget or to counter the logistical inertia just because the circumstances change.

I think Pakistan had important oil pipelines, but am not at all sure