The special thing about a government backed currency is that it is government backed. It heightens the trust in the currency so it doesn't just go up and down and disappear without warning. Bitcoin does all that and more, and it's the MOST stable cryptocurrency. There is regulation and process with government backed real currencies. There's fake regulation and imaginary process with cryptocurrencies. Bit coin is on an ever fluctuating bubble and the only thing that would make it a solid currency is if some stable legitimate economic entity decided to back it. This does not need to be a nation, although something of equal foundation is necessary. If the internet weren't a disjointed mess, it might work. And yes, the internet is a disjointed mess. Not a bad thing, it just means it isn't a stable reliable source of currency backing....
In order for cryptocurrencies to be taken seriously, they need stability. Value is NOT stability, and just because bitcoin is worth 98y45967 per coin doesn't mean squat. It's the difference between a stock and a currency. Stocks tend to rise and fall at the whims of people, where as currencies tend to stay stable unless something really extreme happens (see: hyperinflation, war, severe depression). You watch the value of the dollar drop, and it's dropping slowly and steadily. Well, relatively quickly, but steadily. It's not going up and down and all around. Bitcoin goes through booms and busts on an hourly basis.
And finally, the internet gets bored with things. So what happens when the internet decides its bored with bitcoin? What happens if it just shuts down? A real currency can't do that. It's not that it won't, it just can't. Cryptos very much can just stop being worth anything.