Speculating here but if you look at the price graph this year it looks like someone was trying to prop it up and keep it above $6000. Maybe tether/bitfinex or the Chinese miners, dunno. But anyway this would require $17m or more coming in to the market each week to cover the mining rewards. Maybe that dried up and the buyers ran out of money, then once it broke people tried to sell out before it got worse?
I guess you don't really know unless there is some inside type information. Often currencies are officially supported by governments but with bitcoin the parties seem secretive.
