I find it difficult to understand your response, it's like saying things aren't supported because they're not supported.

The EMV consortium protocol for contactless payments is the same at all payment POS terminals world-wide.
Google Pay and any other contactless credit card payment method works in exactly the same way in India as elsewhere too.
Whether a particular merchant accepts contactless payments or not, or whether there are local restrictions on the transaction amount, etc., are not relevant here - and similar constraints exist in every other country.
In fact a US-based Google Wallet (Google Pay) does not block you from using contactless payments in India at all - as mentioned up-thread, it's just that the interface changes and one can no longer see all of one's saved cards or switch between them. Only the default card continues to be used. This is the puzzling part that we are discussing in this thread.

For now, the only "solution" is to ensure you have your desired contactless payment card set up as the default in the Google app before you enter India for a trip.