It's quite simple really, no predator hunts herbivores that are faster than it is.
After all, there's always a short chase before the prey is 'caught' and the fight begins, if the herbivore was faster than the predator, they'd simply outrun them. Since we have smart predators, they don't even bother.
Wild mektoubs are faster than any predator, thus nothing hunts them.
Some more interesting examples of this: Gnoofs are faster than any predator except cuttlers and kinchers, so only cuttlers and kinchers hunt gnoofs. Since both are so fast and the gnoof is only slightly slower, a cuttler can chase a gnoof over a very long distance before finally catching it.
Jugulas on the other hand, are some of the slowest predators, so there's not much they can catch. Lucky for them, every region that has jugula also has yelks, otherwise they'd have nothing to eat.
It'd be neat if we had some predators that could catch prey in a way that wouldn't require chasing them, like laying a trap or something...