People will only consider using Bitcoin as a mainstream currency when it is completely accepted in the financial market.
Bitcoin is already accepted in the market, the people who are still skeptical about the capabilities of bitcoin needs to get out of their shell. Bitcoin is the future of the market as a whole. The only thing that makes it look like not accepted is the accesibility and knowledge of bitcoin. If people where to be paved a way to acces bitcoin and educating them about the wonders that it can do then more and more will continue to favor bitcoin as opposed to fiat.
Also, the coin is currently too volatile to be a mainstream currency and hence is not a trustworthy exchange means. The coin has to be more stable for the people to do so.
Volatility is a very daring but acceptable word, bitcoin price can suddenly collapse in a snap but think about it, bitcoin has a limited supply and there is also a halving, which can guarantee that there will a skyrocket in prices. Unlike fiat which can be printed endlessly, bitcoin is a vacuum that will suck the value of fiat. The only disadvantage of bitcoin is that it doesn't have a dividend like shares in stocks.
Right now, the coin is a great investment asset to earn good profit returns but is not fit to be a currency.
With the current price of bitcoin, I can agree to that but if you broaden your perspective and think about other people empathically there will be differences. If bitcoin can help in buying more items that you need for sustenance compared to your countries cryptocurrency then you would obviously choose using bitcoin.