Why is Bitcoin tied to Fiat? Why is Bitcoin value moving like a stock? satoshi said the value will be derived by the limit of total coins. But we are seeing the opposite. Why dont we mathematically calculate the value of bitcoin according to the amount of bitcoin mined?

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Agreed Value * Bitcoins Mined = New Value

0.0010 * 1 = 0.0010
0.0010 * 2 = 0.0020