The strength of a network is n^2:
https://en.wikipedia.org/wiki/Metcalfe's_law
It makes sense that the more people leaving a network then the utility of said network will decline.
What seems odd is why they care if people move to Insta or WhatsApp, since FB owna both.
Tried removing Whatsapp for something like Telegram but couldn't since I need to convince my parents and sisters and gf and friends to move there too.
I'm also struggling with this issue and I've been contemplating about either moving all of my interactions on a mailing list or a mastodon instance. I don't know how to move the network of my friends into that space.