The difference is that all of them work cross devices. That's why I only get video calls with WhatsApp and I never get one using one of the many video call apps

The difference is that all of them work cross devices. That's why I only get video calls with WhatsApp and I never get one using one of the many video call apps of Google. I learned today, by reading this thread, that somebody could have sent me a link to a Facetime call. I never got one. Everybody in my country use WhatsApp for video calls (maybe somebody is videocalling with Facebook Messenger or Facetime, very few with Telegram) and nobody has to worry about which mobile OS the other person have. WhatsApp has commoditized both iPhones and Androids here. When people choose to buy a phone they don't think about how they'll make calls or send messages. They install WhatsApp, because they have to or they won't call and message a lot of people, and the problem is solved. Edit: by the way, probably every single phone has builtin interoperable 1 to 1 video calls from the days of 3G. I remember testing them in late 2002 / early 2003. They worked and probably still work unless they retired the standard because everybody is using apps.