What is behind it? Speculation I think. In my opinion, it is the main reason for market volatility. And like everything in our life, this has two opposite sides. Right now we see bad side of that - market downtrend and as a result total panic, grim mood, disappointment, frustration, crypto-depression.
But because of the same manipulation, we had such a wonderful summer and autumn 2017! When my bag did x10 even without any help from my side . And taking all of that into account, it isn't over yet. There will be other pumps and dumps, we just should be ready and keep our eyes open.