Facebook / instagram / messenger, from what I can see, are just hard charging innovative platforms trying to create products people like. Their businesses could crater pretty easily and the only reason it doesn't is because they keep trying different things.
It's not like search and microsoft's OS dominance / network effects from their Office products.
You don't need to log onto facebook in order to work, you chose to because it's fun and you can connect with friends. Google / MSFT have far deeper hooks.