My mother didn't really have a common means to communicate with her grandchildren in the same way.
Email, phone are just not the same.
There are more channels available now for sure, but none so ubiquitous.
Facetime is not displacing FB for a lot of things, but that's more direct.
'Everyone is on FB' is the reason it still holds in these kinds of uses cases.
None of us case one way or the other about the platform, we'll just use what's convenient, but that is what it is.
This is a very common theme among FB users. FB by the way, is still growing it's userbase, and growing revenues even more so. The themes we see here on HN and even in the news don't represent the views among the population, nor are they necessarily very close to material reality.
My extended family uses FB to share info about events.
This, and other pedantic activities are really common around the world.
Don't reduce the material reality a situation to a meme that that represents a personalized view.