The reason that Facebook and Twitter receive this scrutiny is that information posted to them is public, persistent, viral and forced into many people's view by feeds. I think SnapChat counteracts all these features.

I was recently hanging out at some nightlife spots, casually talking to random millennials at bars and such and realized that nobody was using Facebook or Twitter. They were all using SnapChat, almost compulsively.

I asked them why and they said it was because their mom was on Facebook (!public). They also liked that everything disappeared after 24 hours (!persistent) and it alerts you if people screenshot your posts (!persistent). They also liked the fact that you couldn't repost stuff, only show pictures that the app took and you only shared with your friends (!viral) and only had to look at their stuff if you actually wanted to (!feed). It didn't come in on a feed.

I think Facebook and Twitter are going to be cleaned out soon except for self-promotion and commercial information. At this point I assume that Facebook is public too. People desperately want privacy. I think a rising trend in the industry is the notion of forgetting. People want services to forget. They want to live in the present and not have everything remembered about them forever. They also don't want to be bombarded by feeds since they are full of distraction, advertising and ideology. The only thing they are interested in posting to these public services is things that they want to share publicly, like self-promotion or commercial/job related stuff.