Active enrichment from trainers only goes as far as when the trainers are actually doing it, but in the case of big cats and apes with big enclosures, the landscaping allows for far more stimulation than throwing a ball into an undersized bare water tank.
And like Jcardona said, just because you can, doesnt mean it should be done. Obviously my opinions arent absolute truths, because they are just that - opinions - but that's my reasoning, and in my mind, it's sound. You obviously cant recreate the wild in captivity, but with animals like apes and big cats, you can come a hell of a lot closer than you can with Cetaceans.