https://imperfectplan.com/2020/01/24/the-money-el-salvador-uses-as-currency-usd-dollars/
Venezuela is the country whose national currency has collapsed.
Using Bitcoin as a payment currency benefits them because it is
If their national currency was strong there would be no need for Bitcoin.
Nigeria is a developing country in Africa and its government is concerned that Bitcoin devalues its national currency. Bitcoin is good for the people but overall it is not good for their country when the crypto-related crime is hard to control.
The problem with Nigeria are the continuous Bad Government the country has had. Up till now there are still repatriating loot from previous past government whether it is at the National or state level and non of this loots were taken through cryptocurrencies.
It is the same way you believe that Nigerian government think's Bitcoin will devalue it's national currency that's the same effect Bitcoin will have on the El Salvador currency even though you think they use the same US dollar but this has not helped them in anyway and all the devaluation the the Nigerian Naira has had is not from nothing related to cryptocurrencies.
The thing to understand here is, if the government of a country is willing to take care of their nation like what the El Salvador President as done now, they could be seeing good change to their economy and I hope it works out well for El Salvador.
El Salvador is a poor country and they use dollar currency instead of their national currency. They used to have their own currency but it was replaced in 2003 by the dollar. 70% of the people of El Salvador do not have a bank account. Therefore, the application of payment in Bitcoin is quite suitable. They will not need to develop complicated infrastructure like banks.
Nigeria is a country with the 25th largest economy in the world (as of 2021 according to https://en.wikipedia.org/wiki/Nigeria). They have their own currency and banking systems around the country. The presence of cryptocurrencies will threaten their economic momentum as well as their national currency. There are a lot of fees that they can get if using the national currency so they will take advantage of that instead of Bitcoin.