Good point. But It's hard for any country to switch to bitcoin completely.
They don't need to completely, switch, but they can buy bitcoin to hedge the inflation rate.
With their money in bitcoin, that would be safer compared to their fiat money, and that will make bitcoin a store of value as people believe on it.
Bitcoin will not be the main currency, for now it's just an alternative, and remember it's not yet scalable, so that would be a big hindrance for now.