Is it because you have to get somewhere? Is it because you're an ex-F1 driver? Do you enjoy the game of cat and mouse? Or is it something else?
For me it's because I have to get somewhere; it's easier to primarily look ahead and not have to worry about someone coming up on you vs you on them; because the speed I'm comfortable at is above the posted limit; and because the cat and mouse game keeps me much more alert to my driving.