Apple Pay has not been introduced in India for a variety of reasons. We should first note that our banking system is different from other countries. As far as my knowledge goes, our banking does not even approve debit card payment requests from third party without initiating it ourselves every time. That is in most of the foreign countries, debit cards can be used to make payment for iTunes purchases. Banks have opened up to that option but where as that is not the case with India. Similar situation is prevailing for Apple Pay as well.
Moreover Apple holds a very little market share in India and though it is a strong company it still has not got much brand recognition in India compared to other countries