Prey drive is awesome when you have a policy or military dog, great to have that trait on those dogs. Makes it also easier to train.

Now, the OCM (Olde Cape Mastiff), its main role is to be a Farm dog, property protection, good with family, defence drive and velcro dogs (stay close to you), that is why they were bred for by the frontier people of Southern Africa.

In all those reasons above, prey drive is actually undesired. Dogs were kept with the wife and kids while the men went hunting, or to farm. As as then, as it is now, the land and its people were unforgiven. Any dog that did not fit the bill was just culled.

So imagine you had a toddler running about and prey drive kicked in, the dog would give chase. What you think it would happen? The farmer would just shot it. The dogs were bred to be family protection dogs foremost.

Or you go to the bush hunting or doing your work, and a dog sees an animal, and takes chase. Now you alone, open to attack either by wild animals, or native population. Why would you want to keep such a dog?

That is why prey drive was, and it still is, undesirable in the OCM.

You want prey drive, get a Malinois. The best there is for the kind of work that needs prey drive.