It's pretty much well known that their public wallets are now empty and people could see them getting lower each time they dumped. 
This is antecedent and coincidental but my observations, at the time, there was a correlation between Ethereum dumping BTC and the $Fiat value of BTC plummeting.
Maybe that is indication that the Bitcoin volume is largely faked in the bear market (bots trading amongst themselves) and when $millions do legitimately get dumped, the market can't sustain it and thus has to correct to a lower price.