It's not an easy question to answer because there are unfathomable reasons why a market moves. I have touched on this in other comments, a lot has to do with trend lines and what is psychologically seen as support, etc. Bitcoins rise was parabolic at the end of 2017, people bought in at all different levels as it was rising, investors, speculators, traders and general people like FOMOers, etc, all bought for different reasons and have different strategies, whether good or bad. The market is a living breathing beast, many people will still be holding who bought in at the top, along the way down many will have given up hope and sold, many will have levels at which they are willing to take a loss if it rises to $9k, or $12k for example, many will not sell until it reaches $20k and they can break even. Then there are traders and speculators buying dips and selling rallies to make coin while the market is moving relatively sideways, some people sell on bad news and re buy on good news regardless of the price and some people purchase each month or week as a long term hold. I imagine many an early adopter who bought in when Bitcoin was just a few dollars will offload some here and there causing big dips too. the possibilities are limitless when it comes to why the market moves in any direction.