Because price is set by demand and the coins actually available for sale, not by the cap.
The 21 million figure is the total supply that can ever exist - but supply alone pins nothing. Something scarce can still be worthless if nobody wants it. Price is where demand meets the float, and three things separate that 21M from real market pricing:
Not all 21M exists yet. Roughly 19.9M mined so far, and new issuance halves every four years. Today's sellable float is smaller than the cap, but it still grows every block until around 2140.
Not all existing coins are for sale. Large chunks are lost forever (estimated 3-4M), and long-term holders simply do not bid at any price. What matters day to day is the liquid float on exchanges, which is a fraction of the headline number.
Demand moves constantly. Adoption, regulation, macro liquidity, competing yield assets - all of that shifts the demand curve while the supply curve is nearly fixed. With fixed supply, price swings come almost entirely from demand side.
Think of it like beachfront land: knowing there will only ever be 21 plots tells you nothing about what a plot costs until you know who wants to build there and how many owners are actually selling. Scarcity sets the ceiling's stiffness under demand; it does not create the demand.
Because price is set by demand and the coins actually available for sale, not by the cap.
The 21 million figure is the total supply that can ever exist - but supply alone pins nothing. Something scarce can still be worthless if nobody wants it. Price is where demand meets the float, and three things separate that 21M from real market pricing:
Think of it like beachfront land: knowing there will only ever be 21 plots tells you nothing about what a plot costs until you know who wants to build there and how many owners are actually selling. Scarcity sets the ceiling's stiffness under demand; it does not create the demand.