That you generally can't gain places on Sunday, only lose them, is precisely why they don't need more mileage on Sunday. Drivers have found their speed and classification by then. If some rallies were twice the distance you'd be waiting for fails, not anybody finding speed.
I get the nostalgia, it suits the times but I'm not sure what endurance is necessary for these days. It served a purpose in the 70s because manufacts were using what they sold, and driving was an art not a chore.