In a self-contained fantasy economy with no attachment points to the real world, this might be compelling. In practice, the rest of the economy, society, etc. doesn't operate in a self-sovereign way, and neither do you.
It's not much different than the problem of micronations[1]. Exciting as they are for D&Ders of a sort, they aren't real nations for the simple reason that they lack a defining feature of a nation (among others): that everyone else think they're a nation.
Cryptocurrency is perhaps not as extreme; a reasonably large number of people appear to be persuaded that units of cryptocurrency are a real asset, and some begrudging convertibility into other kinds of assets (a defining feature of a currency) does exist. Still, it suffers from a similar problem, in kind if not in degree.