Facebook is following the same playbook that a lot of mobile games are doing. They don't really care about user attrition because most users are low-value. If you're just checking Facebook once or twice a day, you're probably not worth the server time cost to Facebook. What they really are trying to do is target high-engagement users ("whales" in mobile game developer slang) and make the service more addictive for them.
the problem with this analogy is that when you lose a lot of users, you lose the network effect. so even if a user is low-value in terms of their actual engagement, they bring value by luring others in
