You encrypt it, and someone can still potentially get it, even if the probability is miniscule. Maybe the algorithm is discovered to be flawed, or they see you type your password, or they install a hardware key-logger, or while it would theoretically take thousands of years to brute force it, random chance has them guess the right sequence on the first try (it could happen). You wipe the data though, and there is no chance for anyone to get it.

Encrypting it is definitely a good idea, but not as a replacement for wiping it.

I wonder if it's because it creates a market, or expresses demand for the real thing. People may be more likely to force the real thing upon children because they can see that people are willing to pay for fakes. Better to try to eliminate the whole market, real or faked, so that there is less incentive for creating it for real. Just a thought.