Why it is that Bitcoin is not accepted in our country (Nigeria)?
It is either of this two, maybe because was banned by your Government for some reason, or maybe because bitcoin is not popular in your country. But as long as you know that sites where you could earn bitcoin, means you could earn bitcoin even though bitcoin was banned in your country and so on. But if you mean by not "accepted" is when you are using it on buying things, it is because your Government is not declaring bitcoin as your currency.
It is not banned in Nigeria. I don't understand why OP felt so. Government of Nigeria only have banned banks transactions in Bitcoin or any other cryptocurrency. Which is rare a case for any bank in any country.
Instead the Deputy Director on Banking and Payments System has himself said that Central bank cannot control or regulate bitcoin. Central bank cannot control or regulate blockchain. Just the same way no one is going to control or regulate the Internet. We dont own it.
Bitcoin is very much legal in Nigeria. There is utility issue as still not many vendors accept Bitcoin. But so is the case with many countries.