Other people are talking about supply and demand.They are right,but i have other point of view.
If there was only one buyer of the entire btc market and that buyer is willing to pay 1 million US dollars for one bitcoin,the market price of one btc would be 1M USD.Sound`s crazy ,but it`s true.
It`s like buying a rare painting.Some buyers are willing to pay 100$ ,others are ready to pay 10 million USD.
Bitcoin for me is something i can determine as mine worth full yes its not physical but it can be more valuable than anything matters in this world that only me and my wallet has the right to handle