in my opinion, why is bitcoin never a global currency, because every country already has its own currency, if you want to put bitcoin in it, of course there is a process that involves the entire country. If this is the case I find it difficult to make bitcoin a global currency ... !!
Added to that, not all countries are in favor in cryptocurrency, yes they might want crypto, but just means as payment solution, alternative money transfer for fast remitting or money, can be a form of investment but not as a global currency, although I would love too, still we know that it can't happen as of the moment.
I can say that bitcoin can be our global currency if we adopt the technology that is using bitcoin as payment so fast because not all country is not that rich, and also not all people really know bitcoin is. So we should spread more of it so that many people will use it or even buy it, tell them how bitcoin beneficial to everyone, and how it is helpful to any transaction we are making. If we can adopt the technology so easy, it can actually happen, but I think it is not gonna happen if the government dont want it to happen because they are regulating it since if we use bitcoin they cannot get some taxes. But maybe they can if they make some law about it. It is actually hard to say.