In my experience most people have at least one other chat app installed. Signal, Telegram, Facebook (I think there's a built in messenger), discord, and snapchat are all common. It's just that practically everyone has Whatsapp, so that's the common denominator.
Not only does Facebook have Messenger, but it's actually a (pretty) good privacy option. It went full on default end-to-end encrypted a couple years ago. Telegram doesn't do that, you have to jump through some hoops. Signal does but it's honestly pretty niche. Everyone from your grandma to your kids has Facebook though and somehow Zuckerberg decided his data-Hoover shouldn't extend to everyone's conversations. It's surprisingly good.
