The race's setup is horse-friendly as well: Shorter than a regular marathon by a few miles and on flat terrain. A longer distance on hillier terrain would be won by humans much more often.

There was an interesting article a couple of years back, positing that the years that humans won coincide with unusually warm weather. The takeaway was the humans have a superior cooling system for efficient long distance running, compared to most animal's superior sprinting capabilities.

I believe only humans and dogs hunt via stamina. You can walk a horse to death or simply chase an antelope until it overheats and dies.