But if you want to communicate with somebody else in an encrypted way, then you can likely do so with effort that doesn't even approach a hobby. Setting up a system requires more effort, but these singular cases are hard enough to detect and crack that the law enforcement agencies would never be able to do it. You might not even need encryption, because you could communicate in ways that are just obfuscated enough that nobody's going to check. Eg write with blocks on the ground in Minecraft or something.

If the goal is to catch malicious people that are trying to hide their communications, then outlawing encryption won't work. But it will give the government a good excuse to spy on people.