In high end sports cars, why are the rear brake rotors smaller than the front ones.?

in most cars with front wheel disks, 85% of the stopping power is on the front of the vehicle, hence the need for larger rotors in the front, especially vehicles with front wheel drive because all the weight, (motor, drive shafts, and transmission) are in the front. for vehicles with rear disks, it gives the vehicle a little better stopping power than regular drum brakes.

In all cars, regardless of manufacturer, the rear brakes are always made less effective than the fronts. The vast majority of braking is done by the front wheels, as more often there is more weight over them, and the weight "transfer" is to the fromt under braking.

If they are made too large, the rears would lock up, as the rear "lifts" under braking.

If you want to demonstrate why they're smaller, disconnect the front brakes, and try stopping the car rapidly!

Or just pull on the emergency brake/ parking brake instead of pushing the pedal, provided the emergency brake is acting on the rear wheels.

Make sure you do it in a safe place, for when you go out of control.

in all cars the rear brakes preform less of the stopping power than the front breaks do. As forward movement is slowed the force is transferred to the front wheels. Same as with a performance vehicle the rear tires usually larger to increase traction during acceleration.

more load and heat transfer in front. Usually they are vented with fins between the plates that help disperse heat away from the metal, where the rears aren't.

More stopping power to the front.