That’s precisely why they’re smooth. Regular tires waste a lot of their potential road-grabbing surface by having grooves, which act like gullies to channel out rain and mud.
But racing cars usually compete in good weather, so the rain-and-mud grooves aren’t necessary. They’re just wasted space that can better be used to add more road-grabbing rubber for better handling in turns and better braking response.
To get even more road-grabbing surface, the tires are made much wider than those on your family chariot. And they’re made of a softer rubber that wears off like crazy onto the track.
You think you don’t get good tire mileage? Why do you think they’re always stopping to change tires?