Possible troll but if not:
First of all, its a racecar, so efficiency isn't their main concern. Second, if I'm not mistaken, these cars are usually, if not always, lighter than production cars. Third, if you did a little more research, you'd know that one of the racers in the field, "Monster" Tajima, is driving a totally electric car. Finally, roll cages save lives, so I don't know about you, but I think they're sort of necessary.