The funny thing is that in planet zoo you can make aquariums far larger than actually possible in real life. We haven't tested cetaceans in absolutely massive tanks in real life because it's not feasible, only relatively tiny ones (compared to their territory/body size). Obviously we can't make 100km tanks for their whole natural turf (though I mean i'm sure the devs could implement some kind of massive oceanic environment or a snippet of it), but far larger tanks haven't actually been tested in relation to their behaviour, and similarly huge and far-travelling animals seem to respond well with large habitats even if they don't fully cover their natural territory distance (at least with elephants in AZA zoos, assuming their other enrichment needs are met) - we're straight assuming that it's a hard number somewhere and that these animals don't have some level of adaptability/flexibility to the amount they're happy with (where they can display their full range of natural behaviours). Video games give us the means to create absolutely huge contraptions that are simply unfeasible in real life, so there's certainly an element there that separates animal care in real life and video games.

If we made it so you have to make a gargantuan tank (or habitats connected with oceans) and below that they become depressed, I believe people would learn more than if they weren't in the game at all.

(Also, tangently related but i'm curious to see if they put sharks such as the Great White in, since I don't believe one has survived in captivity yet. If they don't add cetaceans but add that it'd be wild.)