Clearly people do use snapchap, so either you're right and they have hundreds of millions of insane people, or you're just clearly not the target demographic.
It’s more likely you’re missing something and they do have a user demographic that is strongly entrenched. Of the users they do have they have strong user activity.
Take my 11 year old sister. She primarily uses snapchat and I can’t see her ever switching. She definitely doesn’t shop around these apps based off of some pro/con table of features.