Why we can’t use Apple wallet in India

See the following Apple articles:

Countries and regions that support Apple Pay

Countries and regions that support Apple Pay - Apple Support (EG)

About billing for Apple subscriptions and media products in India

About billing for Apple subscriptions and media products in India - Apple Support

Payment methods you can use with your Apple ID

Payment methods you can use with your Apple ID – Apple Support (UK)

India

• Apple Account balance (from adding funds)
• Net Banking (adding funds only)
• UPI (adding funds only)

Then use / pay with your Apple Account balance, see: Add money to your Apple Account balance

Add money to your Apple Account balance - Apple Support

It's not yet supported in India and other countries.

This list contains all Countries and regions that support Apple Pay - Apple Support