As someone who quit WhatsApp a while back when there was a big scare about a change in ToS (and everyone was promising to jump ship to telegram/signal), I cannot overstate the importance of the network effect. For a platform with a userbase this size, the critical mass of users required to pull everyone over to a new platform is simply massive. I'm on both other platforms, and although I see many of my contacts there, they are simply not active. They prefer WhatsApp, and unless something cataclysmic happens, they'll remain there.