My opinion is that through domestication, humans rather than natural selection have exerted certain pressures on the birds we keep. For instance, many years ago I had a breeding flock of Rhode Island Reds. One of the young pullets went broody and I allowed her to incubate her eggs. She incubated the clutch faithfully and was a very diligent setter. One morning I walked outside and from a great distance I could hear the distressed sound of baby chicks. When I reached the fence there were two chicks alone with the adults just roaming around not paying them any mind. Without warning the pullet that had been setting would dash across the pen to pick up a chick and sling it around before slamming it into the ground and moving away. I rescued both of the little ones who had been completely scalped and ended up passing away. The rest of the eggs had been abandoned. Now if that had happened in the wild, that hen wouldn't be passing her genes and instinctual behavior along to the next generation. That behavior would effectively die off with her. By artificially incubating and hatching her eggs however, I was potentially propagating the behavior in her offspring.
If you've ever read Micheal Crichton's The Lost World the situation is similar to the velociraptors on Isla Sorna. They were highly intelligent animals that had a complex social structure. Being raised without parents to show them the correct way to behave (think about the structure of a kill site in Africa, how a pride of lions or a pack of hyenas behave, who eats in what order, ensuring the young get to eat, etc) the raptors were highly aggressive with one another, there was no organization once kills were made and it was every animal for itself, to the point where they struck out at one another with a ferocity that resulted in the death (and consumption) of individuals. Very few young made it because the parents didn't care for them or actually preyed on them.
Another real world example would be a friend of mine who had a German Shepard. He was a young male. Her sister got a miniature dachshund puppy. The dogs were out in the back yard together so the puppy could go potty. Her father threw some scraps out the door and when they went out a few minutes later to bring the puppy inside, it was in pieces, having been torn apart by the German Shepard. That is a trait that would be quite rare in the wild. Watch wolves (or any wild canine) eating with young pups. They use body language to teach the youngsters their place in the social structure of the pack, but if an animal actually attacked and killed their offspring (like my hen) they are effectively removing their own genes from the breeding population.
So I've said all that to say, that guineas in the wild are probably great mothers despite the hardships they face when raising keets in a wild environment complete with difficulties from weather, predation, resources, etc. In captivity, or an artificial environment, the fittest, or most survivable birds are not necessarily selected for breeding by us. Therefore guineas in captivity may be great moms with large and successful clutches, moderately successful, able to raise a few keets to maturity, or abysmal mothers, not able to set or raise keets successfully. Some of that is because the "best", or most "reproductively fit" are not the only birds breeding, but also because we don't keep guinea fowl in a manner that reflects their wild state. Or environment and climate are usually much different than the areas they inhabit in the wild. And guineas are no where as domesticated as chickens are. They still have habits and instincts that have not been bred out of them. Those war with what we try to impose on them and can also create issues for a potential broody hen to raise a clutch of keets.
