Bitcoin is actually the currency that can't replace fiat due  to deflation and it is not visible for many users  since they might know how their personal finance works but they have no idea about global economy.
Low inflation is helpful for economy because it makes your goods more competitive on the global market  (for example: due to lower tier countries are accepted to eurozone EUR is getting cheaper and it gives boost for economy). But if you accept only BTC then your products are rapidly getting more expensive. At a single moment the entire export might become non-competitive for the market that would cause insane loses.

Cases when BTC prices are recalculated to USD are not considered since here it is just a substitute for fiat price, not a replacement.