I don't know what cohorts Facebook is looking at. Are they seeing a drop in engagement but balance it doesn't matter because of the revenue stream from advertisers? Or may be the bulk of users have increased engagement with a non-chronological feed? Perhaps more users than I realized follow over 1,000 users and the chronology value was lost a very long time ago.
Oddly enough I'm finding myself returning back to RSS feeds. Lots of excellent independent bloggers still out there who actually write useful things. edit: and photographers.