The bad UI generates a sort of viral effect. I know a lot of young kids who use snapchat and often the conversation starts with 'How did you do that effect on that video?' or 'How do you send a text message without a picture?'. Snapchat is one of few apps that has a lot of hidden features for power users that are not explained anywhere. I am not saying that it is a good thing, but it makes people talk about it.