Bitcoin marketprice is decided in supply and demand in the market, if you're familiar in exchanges you could clearly see the buying and selling section, it is not controlled by bots or code, etc. but it depends in the investors that are buying and selling bitcoin in the exchange, When a lot of investors selling their bitcoin in the market it is going to result to a drop in the market price in bitcoin, also when a lot of people buying or investing in the bitcoin market price is going to increase or pump. The demand is going to increase when no one wanted to sell their bitcoin in the exchanger, that just means in the buying section it would be in a higher price because people would want to buy bitcoin it needed to increase their buying price if they wanted to buy, if you set the buying price at a low market price it will be placed last in the buying section. Also in the selling section in the exchange, if you want to sell your bitcoin and set it at a certain price you need to wait for a buyer, other selling is going to sell their bitcoin lower than the price you set decreasing the market price.