Both of the reasons you state have been things I've heard, so it seems reasonable but I think there are many other factors and I would hesitate to waive my hands and declare those as the biggest two.

For example, Bitcoin Beach was pretty influential, providing advocacy and a test bed for Bitcoin usage and adoption. I imagine they also did quite a bit of lobbying. Maybe they even were listened to more because of their economic success?

Also, from reading Wikipedia, it looks like El Salvador was the worlds leader in remittances (per capita) from abroad, which is a major use case of Bitcoin in its current form.

So, just as likely as reasons #1 and #2 listed above, there could be a "Reason #3: Strong Lobbyist Presence, Including A Community That Is Piloting Adoption" and "Reason #4: Substantial Remittances From Abroad".

I certainly don't know and I feel pretty ignorant when it comes to how adoption actually played out in El Salvador. I would love to hear from someone more knowledgeable than myself on what actually happened to make it a reality.

In terms of other countries, there's been quite a few articles. Here are a few that I've found just Googling:

Some countries that keep coming up are: Brazil, Panama, Cuba, Ukraine. Countries that have high adoption that I don't hear about so much: Vietnam, India, Indonesia, Malaysia, Philippines (src).

There were rumors of Brazil making Bitcoin legal tender, but it looks like those are mostly false and they're just trying to just regulate Bitcoin.

Vietnam is apparently extremely high in adoption and I'm failing to see why. Maybe something about China banning mining and miners moving to Vietnam? Some other reason based on mining and cheap electricity with access to hardware? I really have no idea.