WhatsApp and WeChat are so commonly used that they have become kind of de facto standards for messaging, since both can run under iOS and Android. Especially WhatsApp, which is very popular worldwide except for parts of Asia where WeChat dominates.I know people with WhatsApp or WeChat, but I literally don't know even a single person with Telegram or Signal even installed. But I don't have either WhatsApp and WeChat installed because I don't want to have to load 5 different messaging applications. Therein lies the problem.