So, for a country like India, it's possible for the government to ban gambling and restrict citizens access to any gambling site, only those who find their way around the use of VPN can access gambling site..
You are overestimating the Indian government way too much. They are competent, but not that competent. They have banned porn, crypto related stuff etc, but people over there still use them pretty easily and many of them aren't even tech smart.
I have several Indian friends which is how I came to know about all of this stuff.
This is exactly like in my country where they prohibit but do not completely prohibit several internet providers here, for example the internet owned by the government and non-government is different, meaning that nationally the internet used cannot access gambling sites but it is different from the non-national internet which is not collaborating with the government, I can still access gambling sites without having to use a VPN, actually the only problem is that it is prohibited by my government but I can still easily access gambling sites unless the site prohibits users from countries where it is not allowed, maybe it's a different story.
I often see that many Indian people can still access sites that are prohibited by their government because several of my acquaintances have never had problems with them accessing sites that their government has prohibited, not only cryptocurrencies, maybe even gambling sites, but again it depends on how the user uses their wits to To access this gambling site, you don't have to use a VPN as a quick step, look for other ways that are safer than using a VPN which might lead us to have problems with gambling sites if we use it.