There are 3 main reasons why you should only use online casinos in Indian Rupees. It comes down to:
Legality
Affordability
Convenience
Online casinos must accept INR in order to legally offer their services to Indian players. Furthermore, it's cheaper and more convenient to use online casinos that accept INR, because you avoid having to deposit foreign currency, pay conversion fees, and so forth.
Click here to learn more about why you should only use INR casinos.