Most cracked brake rotor problems can be traced back to drivers or pit crew who dont take the simple precaution of rolling the car back and forth over one complete wheel rotation for several minutes when it arrives back at race end, this helps prevent caliper/pad localised heat soak from warping or cracking the rotor. Having a driver who sits in the pits with his foot planted on the brake pedal for the entire pitstop duration is another sure way to ruin an otherwise good brake setup. Running the slow down lap without using the brakes at all helps as well.