Purchasing power has always been the main reason for the impact of cryptocurrency prices, and these purchasing power is often affected by the outside world, such as news, hackers!
I dont think that only purchasing power is the reason for ups and downs; there are so many other factors which affect price of bitcoin. Due to whales price will not always increase because when they want to buy bitcoin, the price would drop and when they want to sell the price will go up. Trust is also an important factor for up and down of bitcoin price.