Now also Strava is making their feed sorted by some magic with no option to make it chronological :( I can't quite understand this trend.
Say you pick the "time to like a post" metric, then as an employee you're incentivised to put the most click-baitee article at the top. Now if you pick the "number of ads displayed in feed without drop-out" you may have something similar too.
Rince and repeat and you end up with the mess we see.
Regarding Instagram, I noticed they started to retain posts from the timeline. So they encourage compulsive checking it the app. Open it once : it shows 2 new posts, close it and open it again, 2 more posts, both old by at least a few hours.
They just rewarded your brain for checking the app compulsively. Once I noticed that I couldn't unsee it, and I closed my account.