Its much easier to defend then attack. And if indian troops were able to enter any of the big cities or towns, they would have to deal with urban warfare the likes they have never seen and likely to have ever trained for. And Pakistani forces have trained for unconventional warfare vis a vis the Taliban and others, while Indian troops, the only real combat they have seen is firing across the LOC or in Siachin, but it really doesnt compare. So the cost of the war would simply be to much. It would only make the situation infinitely worse for them unless the manage to utterly destroy Pakistan, which is unlikely.