Performing a dps rotation optimally requires cognitive bandwidth that often detracts from situational awareness. For casual players, or someone learning a new dungeon, being able to pay more attention to enemy spellcasting, stuff on the floor, timers, and other environmental cues instead of tunneling a dps rotation might be more fun than getting 1-shot by something you didn't see because you were looking at a cooldown or doing crap dps because you're waiting to kick a cast or something.
