Bitcoin is not yet fully payment system like fiat. Bitcoin is high volatile and common people of Afghanistan would not like it. Well devolped countries should choose bitcoin for payments purpose than off course some small countries will also adopt it.
The thing with volatility of BTC is, that many other currencies are also highly volatile.
After the ~20.000$ ATH in Dec. 2017, I remember comparing the falling price to the (at the time) rapidly devaluating Turkish Lira, and unsurprisingly, Turkish people wouldn't have lost anything (I think they were even gaining) when comparing BTC to TRY since they were falling at a similar rate and TRY was crashing even a little harder.
Another example is that central american states often have massive inflation on their local currencies, so they resort to USD or BTC.
Also, the volatility isn't really an issue if you get paid monthly in BTC and use it to pay for expenses, since you roughly "sell" (by buying stuff) at the same time at which you "bought" (got your paycheck). Some months you may even profit off the volatility, e.g. during bull run - get paid on 1st of month and stuff you buy at end of month will be highly discounted for you, basically. Some months you might take a little loss instead if e.g. you got paid on a "price spike" day and the value of the BTC you earned subsequentially falls. But it should even out in the long term really.