The world just wasn't ready for Bitcoin as digital cash. El Salvador acted too early and failed miserably as a result. With mainstream media labeling Bitcoin the "next Digital Gold", most people will hoard it with the hopes of getting rich in the future. Besides, volatility and scaling issues are still at large. Bitcoin can't be used for micropayments because of the "high market prices" and often congested Blockchain network (which results in high fees). The Lightning Network is not even a viable solution at the moment. It's buggy and utterly-centralized.
At least, El Salvador tried to boost mainstream adoption for Bitcoin. Maybe someday, BTC will be used as a currency. Sometime within the distant future. Bitcoin often comes with its surprises, so anything's possible.
Is the world not ready, or is bitcoin not ready and not really suitable to be a currency, even though that was its original purpose? Because as you said, bitcoin is quite volatile and scalability is not yet solved. Meanwhile, the criteria for payment methods or currencies used on a daily basis are fast, free and stable. It is clear that with the current state of bitcoin, it is no longer suitable for use as a currency, especially for small daily value payments.
Many blame the government of El Salvador for acting hastily and lacking strategy, planning. But in my opinion, the reason why people in El Salvador are not interested in bitcoin as a payment method is because of bitcoin's problems.