The guy at my local game store said something about co-op games that I keep thinking about
I was in GameStop in Austin 3 weeks ago and this older guy next to me said "split screen died because nobody wants to look at their friend's half of the screen anymore" and honestly I still don't know if he's right or just being a grump.
Split screen didn't die because of that, it died because consoles stopped pushing local play so hard once online took over. The friend's half of the screen thing is real though, my wife and I used to play Halo co-op and she'd get mad I kept looking at her side. Honestly couch co-op is making a bit of a comeback with stuff like It Takes Two and Split Fiction. That old guy might be onto something but the reason is more about money than eyeballs.