I don't think the implication is that the government is forcing anyone to use WhatsApp, but that in some places it controls enough share of the messaging market that people are forced to use it because that's what everyone else is using.
Remember when it used to be $0.10 or like a quarter per sms message or something ridiculous? Back when you didn't have a proper web browser etc on your phone. You know before smartphones were a thing. The companies were able to hold us hostage for text messaging etc because of that.
Now imagine you live in a country where they tried to do that post smartphone's. Everyone in those countries de facto turned to alternate services like WhatsApp for texting and even calling. So it wasn't like a government mandated thing. But it was more of an effective mandate because of carriers. This includes most of the world outside the United States. Over in Europe. WhatsApp is common for this very reason. South America again same thing. All because of carriers trying to overcharge but forgetting the internet had become a thing in everyone's life.