BRICS isn’t an alliance or a cohesive entity. It’s the equivalent of the G7 for major non-western economies. India and China hate each other. China and Russia only really get along in being anti-US. Brazil and South Africa have no real intersection with the geopolitical goals of the other. BRICS isn’t a geopolitical anything of any meaning.

I suspect India is doing this for the simple reason that they have zero control over Windows while they would have as much control as they want over internal-Linux use. They’re large enough that they can make it work, assuming they’re willing to dedicate the people and the money to it and put up with the non-insubstantial switching costs. Open question on what their follow through will look like, but it’s entirely within their capability.