Stable coins are only a relative term. Stable coins, in theory, must be backed by something considered widely as stable asset, like fiats, golds, and any precious things. Unfortunately, fiats, gold, precious things are not truly stable. They are usually stable but sometimes, they are volatile like what we see price of gold. Fiat currencies are a big joke, and they are only stable on the paper desk, in theory. In countries with hyperinflation, fiat currencies are not stable. One fiat currency is stable today but it will be a trash paper next 6 months.
No fiat currency is stable today, even dollar is not stable.
Also, you have said the reason why stable currencies can not be backed by fiats, gold or any other stock.
Stable currencies are not fiats or gold or any stock and cannot be backed by them, they are like unstable currencies that are not backed by anything, only difference are the prices that are not volatile but relatively stable. Stable currencies should not be backed by anything than increasing or decreasing in the stable coin supply in relation to the demand and selling of the the stablecoin in a way to maintain relatively constant price.
nothing is stable.
period
but sometimes OP or anyone may want to have a currecny that's closer related to their country fiat currency, nothing wrong with that.
it's not a good idea to have 100% of your assets in BTC or crypto because of the volatily, better to have at least some amount in fiat or some currency you'll need on day-to-day