Originally Posted by Chrome Prince

I found this as well, others have said it's their second best day!
I think it could come down to the jockeys over exerting themselves on the Saturday where the prizemoney is greater, and then coming back Sunday and feeling it over the concluding stages.
Imagine the physical toll some jockeys put themselves under riding trackwork in the morning and then racing in the afternoon, some seven days a week.

Also weight comes into it, many jockeys waste to make the weight for a Saturday, and the physical exertion would surely impact on the Sunday.