It is a sort of underestimating the market and it is because nobody is capable enough to move the market wherever he/she wants to go. We can manipulate some coins at it move temporarily but if we talk about Bitcoin, you simply never think about in a decentralized project like this. It was just an assumption that barely not to happen in real scenario. Bitcoin move freely, it pump and it dumps depending on the market situation and demand and supply, not because of someone is controlling on it.