Before being acquired, WhatsApp served a half a billion users on a $1 per year subscription model (first year was free, and they were competing against comparatively high charges for sms), and apparently only a few dozen engineers. Signal manages a similar feat on a handful of (large) donations. It's possible to have a profitable business while charging users a small fee, but once a public company achieves network effects and a captured user base, there is a pressure to milk it for all it is worth.
In a normal market there would be competition and an equilibrium would be reached, but where network effects dominate, it takes something like Signal to make a dent in this regard. That said, there's no reason that a non-profit version of instagram couldn't eventually compete or dominate by charging users a pittance.
In a normal market there would be competition and an equilibrium would be reached, but where network effects dominate, it takes something like Signal to make a dent in this regard. That said, there's no reason that a non-profit version of instagram couldn't eventually compete or dominate by charging users a pittance.