If you own land in the United States, you pay property tax in USD. That's just one of myriad ways that the dollar is backed by the physical assets of the nation.
Now that velocity is picking back up, we are seeing astronomical inflation.
Just because a govenrnment controls the currency doesn't mean it's in your interest to save long-term in it.
https://en.wikipedia.org/wiki/United_States_Strategic_Comman...
But sadly the price increases also attract a different kind of demand, much more volatile (80% crashes now and then).
Bitcoin certainly has value as a medium of exchange because it can be (and is) exchanged between people. A government that accepts bitcoin for payment of taxes adds to the exchange-value of the currency, certainly.
Bitcoin also has some merit as a store of value, in that people observably hold bitcoin with the expectation that it will remain valuable. Ultimately, however, this role of currency is speculative: it requires belief that people will want the currency in the future at a reasonable price. This is also where crypto bulls and bears most disagree.
Bitcoin has a much more ephemeral status as a medium of account, however. Stores aren't pricing their wares primarily in bitcoin; when they accept the currency they price primarily in local currency and perform a spot conversion. This is also what I was referring to above with jurisdictions not assessing taxes in bitcoin even if they accept it.
The medium of account is the least flashy but perhaps most fundamental role of a currency; it provides a backstop of price stability. Repricing goods and services is hard. It obsoletes marketing campaigns, it confuses contractual expectations, and it can require literal printing costs re: price tags and the like. That stability, however, lets people think of one currency-unit as worth something real, not just some amount of another, more important currency.
Bitcoin does not yet have this status, and this is where lack of tax assessment in bitcoin matters. I can't say that (e.g.) 0.1BTC will definitely pay my property taxes for a year, no matter what else happens to the currency in the meantime.