They intervene because they are worried on what will happen on El salvador if major collapsed happen and we can't deny that this events always happen every year. And I can't also blame other country be worried about them some goverments in other big countries doesn't believe the potential of bitcoin so maybe this is a good wake up call to other nation that if this country became successful when adopting bitcoin then maybe this will be their basis to adopt it on their systems.
If a financial collapse occur in El Salvador, then they the other nations need to worry about it? Latin America is full of failed economies such as Venezuela and Ecuador. And in none of these cases, cryptocurrency was involved. If a financial collapse occurs in El Salvador (although there is hardly any chance of that occurring), the Salvadoran public know how to deal with it.