"In fact, empirical evidence shows that markets have not naturally gravitated towards fixed-supply commodity money but have instead shown a preference for flexible, state-issued fiat currencies."

We didn't have much of a choice until recently. Your empirical evidence is only evidence that the state has been successful at violently suppressing competition. Bitcoin has proven resilient and so we now have empirical evidence to the contrary, to the tune of $70K/BTC at the moment.