Why you define it a terrible lock? The fact that I was able to pick it open doesn't means it's not a good lock.

Keep in mind this was a piggy bank where kids put the change got from their parents, so there was no need for security. It was a very clever marketing invention, because only the bank had the key, so you saved some money and then you had to go there to get it open and... very likely you put the money on your kid bank account.

Cheers