Apparently on Virgin Airlines there are chat rooms on the planes. Those have only two practical use cases: dating, and trolling: https://twitter.com/KrangTNelson/status/959907806622121984
I also know folks who have arranged large group bookings (30+ passengers going to the same event) and found it useful to talk to each other.
Whereas seat-to-seat chat is free and relatively reliable.
Thus you can't just randomly message any seat on the plane until they turn it on.