Probably because most of the clay targets shot (or, shot at) in competition are rising- down pitch would put the POI of the load below the rising clay (or pheasant). The possible exception might be the running rabbit target event- not sure of that, however. I'm NOT a serious SC shooter- prefer live birds awing (crows, barn pigeons)-- for my off-season practice shooting.

"The field is the touchstone of the man"..