Just because of the people who want to sell rather than buying. If the sellers are more bigger than the buyers, literally the price will be lowered. But if the buyers are bigger than the sellers, then that's the only time the price will be higher. The price of bitcoin varies about the investors. Sometimes, other people also stocks some bitcoin in their wallets and after some time, they would rather sell it when the price is so high. So that's a good idea to gain profit.