Middle seats are the worst. You’ve got someone on either side of you, so you can’t just lean over into the window or the aisle, and you’ve got two armrests to fight over not just one.
Often the passenger in the middle seat was disserviced on a previous flight. Or they paid the most for their ticket in the whole cabin, buying when there weren’t any aisle or window seats left. In either case the person who may be the most deserving of a better (or at least not deserving of a wose) experience gets exactly that. Over time there have been several ideas floated to address this.