It may be true, countries that have their own currencies tend to have more difficulty adopting bitcoin as a legal currency (based on law) despite the fact that bitcoin is legally used as a means of payment in several countries that have their own currencies. El Salvador is certainly different from most other countries, but that doesn't mean other countries can't adopt bitcoin like them even though they have their own fiat currency.
I don't have valid data on how many countries where bitcoin can be used as legal tender, but it is true that bitcoin tends to be used more as an investment and trading asset than as a real use case. Indonesia is one of the countries that does not legalize bitcoin as a means of payment, but investment and trading are legal.
For me that is a much more rational reason because countries that have an official currency will find it much more difficult to adopt bitcoin as a legal currency. Countries have regulations that regulate the issue of official currency and if we think they want to change bitcoin to legal currency then it must go through parliamentary approval. This is where they will run into problems because there will be challengers from several factions joining them.
Very few countries accept bitcoin as legal tender and if this relationship is linked generally only El Salvador may be legal in the use of bitcoin as a legal means of transaction. Most countries accept the adoption of bitcoin as an investment asset and that is also what my country does with Cryptocurrencies in general and bitcoin in particular.
Well it is indeed a situation that is sometimes very difficult to accept because when a country tries to legalize bitcoin as an alternative payment then indirectly they also have to prepare some supporting facilities just like El Savador did.
But even so it does not rule out the possibility when bitcoin continues to grow then I think it is still very possible for some countries to provide leeway in terms of regulation for bitcoin and it is not impossible for this to be used as a legal means of payment in the end.
I personally actually for now do not really matter whether bitcoin will be used as a legal tender or not in my country because when now the government in my country is starting to accept and provide facilities for bitcoin to continue to grow it has become a very good thing even though currently bitcoin is still considered a commodity but still it is a good thing until now so that when the current regulations are favorable for my country and bitcoin because they still do not take banning action it is very pleasant for me.