Honestly instead of calling El Salvador a failed experiment, I think other countries should learn and study what they could change with what El Salvador has done. If El Salvador suffered from low adoption rates because of volatility, who is to say that other countries such as USA won't experience the same thing should they make bitcoin a legal tender?
However, the steps they took were not bad ones. They only tried to make it a currency, and that is where they started failing. However, I don't see it as a failure. Other things can be done to make El Salvador a complete Bitcoin city. The issue of adoption was not meant to be compulsory, and if it does not work as a legal transaction, they should focus on their accumulation program.
It's just that El Salvador was the first to do this hence why they did not have any references and had to learn this through experiencing it themselves. But now other countries can look at El Salvador and learn from their mistakes. They could find ways to encourage more people to use bitcoin for daily transactions despite its high volatility.
They need to be appreciated because they are the first country to have ever done this, and they have experts who are putting things in place. There was one certain time that they were teaching Bitcoin in their schools, and this is another way to make people interested in Bitcoin. For those who decide to use Bitcoin as their currency, it's a matter of choice because the government can not force it on anyone.