Think of it purely from a practical perspective. Banning technology has a distinct tendency to force the usage of that technology underground. And if any technology is going to thrive when its usage is driven underground, it's encryption. I can't think of anything more perfectly suited for hostile environments. The whole idea is that it makes your opponent's job more difficult. Attempting to make encryption illegal would likely backfire spectacularly in my view, as it might encourage more people to start using it.
Not only is it impractical to ban numbers, it's also an incredibly foolish endeavour. Not least because of the consequences it would have to our everyday security, but also the conflict it potentially creates when the authorities effectively prompt the public into weaponising this tool in order to evade them.
I really think that is precisely why we have not really seen a ban of encryption yet, not only that if at some point governments were able to introduce backdoors to cryptographic algorithms and those algorithms were not able anymore to protect your information as they should, then the algorithms that have not been tampered with will have a competitive advantage, which means that people will use them instead of those that have been modified to benefit the government.
In a way this is similar to what is happening with bitcoin, in which many governments will like bitcoin to be banned but they know that if they do so and then people keep using it regardless of the ban then they will lose credibility among the rest of the population and this could incite more people to adopt it.
