Any UX expert can tell you that every little bit of friction counts. I see that mentioned or assumed every day here on HN, but somehow in discussions about using vs. abandoning Facebook it gets thrown out the window. I might be comfortable with email, you might be comfortable with Slack, but my uncle or my high-school friend who's a massage therapist might not be. Also, they and a couple of dozen other older, younger, or less tech-savvy friends are already on Facebook and comfortable doing things there. Getting them to switch to a different platform is a hard sell even if it's more convenient, and if it's even marginally less convenient then forget it. Ease of use and network effects are both real things.