I think most people stick to 1-2 apps based on their culture and friends. But when you live in a culturally diverse society you end up having to install quite a few (e.g. WeChat for China, Kakao for Korea, LINE for Japan/Taiwan, Whatsapp for India/many other countries, Signal for the privacy expert in your life), etc.

I'd consider SMS as an "app" too, with the limitation of no group chats, and requires a roaming SIM card if you happen to go abroad.