Yet the jockeys were only allowed to each have one horse in the race. Why do they discriminate against the jockeys thusly?

The Worker's Compensation Board won't allow jockeys to ride more than one horse ever since having to pay a huge settlement to jockey Robert (Stretchbob Longpants) Williams following the career ending leg-length incident of 1978 when only one of his horses spooked and ran off the track.