I'll try to explain it very simply, many have written before me. The price of a Bitcoin depends on the demand. Since there is a limit, which is reached in + 100 years, then the situation is different. Today, there must always be more demand than in comparison to the new created coins and the offered coins. When more people buy Bitcoin, the higher the price rises, because the offer is limited. The same happens when the price falls. The higher the supply and the fewer people who buy it, the price drops.