There is also something personally ego-shattering about getting destroyed by another human. If I died 10 times trying to beat a boss in a game I wouldn't care much, but if someone beat me 10 times in a row at a multiplayer game I would be questioning everything.
I actually think this is the same point as who you’re responding to. If the human vs ai factor didn’t matter, you wouldn’t care if it was the human or ai on your co-op. The differences are subtle but meaningful and will always play a role in how we choose experiences