Stocks have real assets and intellectual property, USD has the USA army and economy.
The USA army could be dissolved and the economy could switch to use something else. Of course these events have a low probability of happening but if someone wants to say something else doesn't have a floor because demand could dry up you can't say something else does have a floor even though demand could dry up just the same.
It's hard to imagine, but basically a state does need some level of force to be able to protect property rights. Without that you can't have much of an economy period, nevermind a digital economy.