When the market falls long term. The market has few new investors, the old investors are no as interested as before. Volume is very low. That makes the profit from exchange are reduced ( Huge whales are big exchages )
To compensate for the declining profit. The whales and the exchanges are linked together to control the margin. Currently, Margin has a large volume (Bitmex no.1 volume). That's why most of the time the bitcoin chart are U-shaped
They can be controlled both intentionally and accidentally. There are whales that invest huge amounts of money with the intention of increasing the price of Bitcoin. Since they are aware that the price can be controlled by the rate of demand, they just put in a big amount intentionally and when the price goes up, they will withdraw their money with the profit, causing the price to fall again.
There are people with no bad intention, their plan is just to invest a huge amount of money before the price goes up to make better profit, and when they invest, the price will boost immediately.
For investing huge amount of money, they do that for the sole purpose of getting a lot back from it at the detriment of the weak hands and which makes it easy when indeed the only thing driving the price up and down in speculation.
Assuming there is a life usage and the demand is going up as a result of that, then we would not even be experiencing such moves like this, but for now, it is just what it is and as long as there will always be people who simply want to get rich overnight without understanding what they are investing in, it would make it so easy for them.