India was the land of the Indus and became the term for the entire subcontinent many centuries later. The newer generation of Pakistanis feel emotionally about the appropriation of the term "India" by the new country, much like Greeks feel about the Former Yugoslav Republic of Macedonia being named after a Greek province.
Macedonians have argued there was no country as Greece before the end of the Ottoman Empire. Agreed there was no single Greek state, but Macedonia is now a province of Greece so Ancient Macedonia must be seen as part of Greece's heritage, much like Ancient Rome is Italian heritage.