India already has a cap of USD 250k limit on capital flight by individuals.
Nowadays bitcoin is a common method to escape capital controls.
This law will prevent capital flight by the rich which they earned with the patronage of Indian citizens and escape reinvestment locally
I recall back in the 90s there was a huge influx of "Indian" gold into the "West". It was identifiable from it's high purity and almost orange color, it was being carried out as jewelry and converted into real estate for the most part.
My point being, as long as there is a will to move wealth, the holders will find a way around any restrictions imposed by the state and infact restrictions usually create whole industries based on Enforcement of, and Evasion of state imposed restrictions.
A state wanting to continue to control currency, taxation etc seems like a fairly predictable and compelling reason though. It would be interesting if that's not the reason, but I don't think that we need to search hard for one.
Turning this around, why _would_ a country want to allow people to make anonymous(ish) large digital transactions? This is the same government that outlawed some bank notes in recent memory.
1: https://www.cnbc.com/2021/03/15/india-plans-cryptocurrency-b...
* https://www.forbes.com/sites/leezamangaldas/2018/04/18/under...