Simply because India has huge amounts of mobile devices, and the Indian ISPs didn't get assigned many IPv4 gold rush days when anyone could get an addresses by asking.

Instead they've aggressively rolled out IPv6 and carrier grade NAT where needed

Seems like that's mostly mobile users[1], even in the US the mobile carriers are all IPv6, unlike most residential ISPs...

1: https://www.businesstoday.in/technology/story/india-to-have-...

The question is why China is so low. They must have close to a billion mobile devices only at any time. Other countries aggressively use ipv6 for those, I'm surprised China doesn't. Or Google just doesn't see the real traffic in China?

We had some customers in india that required ipv6 support bc some indian isps are apparently ipv6 only!