I’ll agree that using Snapchat as an example is a challenge because it is somehow perceived as one of the most inscrutable interfaces (at first glance) and is also very successful and popular. I don’t think this has to do with the core demographics at all though. Apple has rolled out 3D touch and there are lots of features including those in iMessage (send with lasers!) that do interesting things when you know about the 3D touch interface to access them.
I don’t believe most people are lazy and don’t want to learn new things, and that most people are more interested or they wouldn’t be downloading new apps or trying new things ever. Maybe younger folks with more disposable time do this more, but it’s unfair to suggest the app economy isn’t already huge and growing and shifting.
As the generation of mobile natives continues to grow up, I think it’s hard pressed to believe that designs will still be as default explicit about every feature as we got used to in the desktop era.