As someone who's never used such a service, help me understand what's so critical about it. Can't people just send SMS? Aren't people on fb anyway, which can be accessed with a container on Firefox?

EDIT: got some answers re SMS. Fine, though that doesn't explain why there is so much overlap/redundancy with social media applications. At a glance, it appears I could do the very same things (groups, multimedia) messaging people on facebook without having to install an app, and if people are on whatsapp they're almost 100% on facebook.

Apparently the "critical" nature of this is the facility of sending high rates of pictures and videos to others. I suspect mere FOMO owing to group-chat being localized there is enough to keep some people from cutting the cord, not the ability to communicate to multiple people in itself. People really are addicted to each other.