Which ones—Cuba, Venezuela, Iran, and Argentina? I don't think Bitcoin adoption is terribly high here in Argentina, but hopefully you can forgive me bringing it up—I live here, so it's the place I know best, and the uses of Bitcoin are pretty easy to understand here even if most people aren't using it yet. And even those four countries are hardly inconsequential in terms of the global commonweal: 170 million people live in them, one in every 46 people alive. That's, like, more people than play
Fortnite or
Minecraft. More people than have bought a Justin Bieber album. Almost as many people as follow Ariana Grande on Instagram. Four times as many people as live in California. We're not talking about some tiny Elbonia here. Anything that affects 170 million people is a big deal for human welfare.
But the utility, or potential utility, of Bitcoin is a lot broader than that.
Argentina is not terribly high on the scale of "people being unbanked" or "kleptocracy". If we take infant mortality as a rough measure of kleptocracy, we're #84 out of 201 countries and territories in https://en.wikipedia.org/wiki/List_of_countries_by_infant_an..., so we're actually better than average. We're neck and neck with PRC and way ahead of India. If we trust the table in the GFMag link I posted, which they attribute to "a just-released study by the British research platform Merchant Machine", whoever that is, there are nine countries with an even larger percentage of unbanked than Argentina, namely, Morocco, Vietnam, Egypt, the Philippines, Mexico, Nigeria, Perú, Colombia, and Indonesia. Each of Nigeria and Indonesia are individually nearly the size of the US; Indonesia is the fourth biggest country in the world. As for India and China, they claim that 20% of PRC's population is unbanked (another unbanked population nearly as large as the US) as well as 20% of India's (yet another).
And Bitcoin doesn't become useless just because you have a bank account. If you're paying a 3% tax on every bank transaction (as we do here), experiencing substantial inflation rates, working under the table, or facing the prospect of an Argentina-style bank confiscation, you have a use case for Bitcoin. Don't tell me it can't happen in the US; it did happen in the US in 01933 with Executive Order 6102, with gold playing the role of Argentine dollars.
To expand on the inflation question, on https://en.wikipedia.org/wiki/List_of_countries_by_inflation... there are 24 countries with a consumer price inflation index over 10% per year, of course including Venezuela, Argentina, and Iran (but not Cuba), but also including Sudan (regular and South), Zimbabwe, Congo, Angola, Libya, Syria, Suriname, Haiti, Sierra Leone, Burundi, Nigeria, Mozambique, Turkey, Pakistan, Zambia, Azerbaijan, Uzbekistan, Ghana, Liberia, and Malawi. You may not care about Burundi but this list also includes the 7th-biggest country in the world by population and the NATO member with the largest military. These countries don't necessarily have "authoritarian regimes" but it's still useless to try to save up money in the local currency for anything more than the very short term; after 5 years you've donated 40% of it to your central bank by way of inflation. Or maybe 85% if you're in Angola.
India doesn't have a high inflation rate by the numbers but it did "demonetize" the savings of the poor in 2016—those piles of rupee bills under your mattress didn't lose just 10% or 20% of their value but 100% of it—and this in a country where hundreds of millions of people have no bank accounts! Most of them have cellphones, though.
Both India and China also have a tendency to limit their subjects' access to foreign exchange in general, and cut it off entirely at precisely the moments when their subjects most need to emigrate to seek work. This is not at all unusual among poor countries; a Bloomberg overview of some of the measures current in 02019 is at https://economictimes.indiatimes.com/markets/stocks/news/fro... though mostly from the perspective of foreign investors.
Now, even if the 84 million Turks (one third without bank accounts) aren't currently using Bitcoin to escape the ruinous inflation rate (15% per year)—the way they used to use dollars before the government cracked down on it—it's clearly a problem many of them need to solve, whether or not their nominally democratic government is an "authoritarian regime". But diffusion of innovations doesn't happen in a vacuum, and it may take a while for Bitcoin or something similar to get widely adopted in Turkey.
So that's the kind of thing that makes me think my Argentine experience generalizes to about ⅔ of the world population, and my US experience doesn't.