[Deganta]

Where I live (Austria), Facebook messenger does not have the same reach as Whatsapp.

Pretty much everyone with a Smartphone has Whatsapp, but there are lots of people without a Facebook Account. These are mostly older people. There are also people (like me, but I know several others) who do have a Facebook account, but don't use it on their phone.

The really nice thing about Whatsapp is the installation experience. Just download the App from Google Play/Appstore. Start it. Confirm your phone number. And you can communicate with all your friends. Facebook is much harder in this regards. Signal is similar, "but network effects".