You appear to be looking for a rational explanation for why users of Snapchat are using Snapchat for what they claim to be using it for, when such an explanatio

You appear to be looking for a rational explanation for why users of Snapchat are using Snapchat for what they claim to be using it for, when such an explanation might not exist. Maybe it doesn't make a lot of sense to use Snapchat just for sending goofy pictures, but that doesn't mean it can't become popular for just that.