Good ink for bad blood
The vernacular idiom expresses emotion far better than it does reason.
Indian and Pakistani media were state-dominated to begin with. Since most of the population is not yet literate, it watches television and listens to the radio, which means that the state is still the great communicator. TV and radio on both sides have been hostile to each other, and there never was any subtlety in the propaganda unleashed on each other. There never was any effort to persuade the people on the other side of the border to look at one's country as a good country. Both sides decided to malign each other.
After 50 years of negative portrayal of each other, populations on both sides are totally convinced of the evil-country-next-door thesis. Pakistan's thesis is simple and ideological: India is inhabited by Hindus who were against the formation of Pakistan, Hindu religion is inferior to Islam, Hindu leadership in India dismembered Pakistan and is still at it. The Indian thesis had to be different because it couldn't attack religion, so its thesis is that of destabilisation: Pakistan is an agent of bigger enemies elsewhere (the United States, China) and wants to destroy India's pluralist society.