According to CNBC, federal prosecutors had launched a criminal probe into the cryptocurrencies earlier this year based on suspicions that their price was being manipulated. I think it might be the main reason behind the price of bitcoin dropping to around $4000, but I also wonder whether it could be that authorities are afraid that Bitcoin and other cryptocurrencies are taking over the financial system since they're now so popular.
Institutional investors tend to sell when they hear news of potential criminal action.
Just be grateful that none of those ETFs were approved - we'd have had a tsunami of retail selling as well!