I agree with you! Bitcoin has no market price stability like currency. The price of bitcoin varies from time to time: sometimes up and sometimes down. So many people who are not bold in investing in Bitcoin don't even dare to invest in Bitcoin. In fact, many countries do not accept BTC
You don't specify which currency you compare Bitcoin with
You see, there are over 200 countries in the world (and counting), while the total majority of them have their own currencies (apart from a few exceptions like Panama and a small number of other massively dollarized nations). And you know what? The performance of most currencies in the world are fucking ridiculous compared to Bitcoin on a long enough time scale, going to outright pathetic in like a dozen of years. Fiat is intentionally made to be depreciating with time, so it is only a matter of time (pardon the tautology)
Bitcoin is insanely volatile for a currency, a currency like the American dollar, British pound, or Swiss franc. But these are crème de la crème among currencies of the world. Besides, Bitcoin is volatile in the truest sense of the word, i.e. its price (say, in dollars) can go down but then it inevitably rebounds, and often with a vengeance at that. This is definitely not the case with regular currencies which can only sink and then sink lower, at different rates -- some fast, some slow, and some collapsing like the Venezuelan bolivar or Zimbabwean dollar