Reading your comment finally made it click to me why cryptocurrencies (specifically Bitcoin) are distinct from a gold bar or other non-currency stores of value. A gold bar is going to remain a gold bar forever, people's perception of its value will change even though the supply will remain mostly steady, but it will stay a gold bar no matter what.
Bitcoin may change in value based on perception, it's supply will remain constant after it has all been mined, but it's existence and integrity relies on a large network continuing to exist.
To put it differently, in 50 years a gold bar is a gold bar, but in 50 years a Bitcoin may have no value because everyone stopped mining and the blockchain was destroyed by 51% attacks.
Bitcoin may change in value based on perception, it's supply will remain constant after it has all been mined, but it's existence and integrity relies on a large network continuing to exist.
To put it differently, in 50 years a gold bar is a gold bar, but in 50 years a Bitcoin may have no value because everyone stopped mining and the blockchain was destroyed by 51% attacks.