I haven't deactivated my account, but I have unfollowed absolutely everything so that I have an entirely blank news feed, and uninstalled the app from my phone to avoid notifications. I still use messenger for communication with friends. For me, it was the realisation that 99% of the content in my news feed was posts by corporate pages. I signed up to connect with friends, and initially I did only see status updates from friends. But over time it became exclusively friends liking or commenting on posts by pages, and I was no longer connecting with people.