Nearly all nations in the world already "use Bitcoin" in the sense that they are capable of doing so for any transaction that they want to do and the currency that they use is agreed between the two parties doing the transaction. It'll never become legal tender because of the nature of government regulation, and it'll never replace legal tender for the same reason.
In poorly developed countries, very little bitcoin is used and maybe not all have heard of it and do not know what to do with it or are simply afraid to try it.
yes they simply afraid of joining bitcoin because they don't fully aware of bitcoin they just need some awareness and some education about bitcoin and need to tell them how can they make money from bitcoin then their interest will grow to join it.
Nah, I actually think that even if people in that poor country know bitcoin very well, bitcoin is still kind of expensive thing for them and due to the fluctuation it will add more fear towards the people in poor country, they're not going to risk their money which is still needed to fulfill their expenses for the sake of bitcoin.
Education or anything towards bitcoin in poor countries is nothing if they don't have any money.