1) What do you mean by 'no infrastructure for that'? no infrastructure for what? Admittedly enough, most third world countries lack in infrastructure but this pertains buildings, roads and etc so I don't see how it's related to the use of cryptos in a country.
2) that's true - but there are in fact a large number of people from third world countries who are users of crypto. In fact, a huge percentage of the population in this forum are from third world countries like the Philippines, Indonesia etc.
3) That may be true but that would only pertain to the minority - and mostly uneducated sector of a country. I believe that in a third world country, the population is educated and would somewhat encounter or hear about bitcoin. The financial and business sector of a third world country would surely know about bitcoin or crypto as well. Third world countries are not totally left in the dark because some have even made efforts to make adoptions or some governments have released statements about crypto because there are users present in the country.