In the same context, you can say that America is not India. These kinds of logics do not work in modern warfare.
Majority of people in Pakistan are illiterate and poor. You can't expect much fight from them. Also, Pakistan is in economical turmoil in these days. You need strong economy to fight wars in modern times. High tech weapons and logistics are not cheap.
Also, size of territory does not matters. It took just 21 days for America to over-run Iraq. It was an absolute blitzkrieg.
By comparison, Iran and Iraq could not over-run each other in 8 years of war.
Also, in current times, capturing territory is not as important as taking care of targets of high value, and strategic, and economical importance.
Good thing is that America has no plans to invade Pakistan. This is a wishful thinking on part of some hot headed warmongers who know little about ground realities.
Already the wars have taken heavy toll on Pakistan. We do not wish for another devastating conflict. Our main objective is to become a powerful and properous nation.