I think it's about tax that Indian government levied on the crypto currency.
Here what I know
Indian government taxed 20% tax on long term crypto investments.its good in my view ,also need to mention almost $3.5billion of transaction happened in last 18 months I think.
Don't forget demonitisation of high currency note also happens in last year also,so there are high chances that many big black money bearers also invested in the crypto currency and might be trying to run away from tax.