Frontier seems to have some weird priorities when it comes to geographical areas...
Oceania got all the essential iconic animals, and now it's got a roster that, while pretty small, is very diverse, with all animals having different habitat requirements. A tree kangaroo and echidna would be nice, but the current roster is perfectly fine with me.
Europe ended up with a fairly good selection of animals considering how underrepresented it usually is in zoo games. Just like Oceania, it has all the essentials for a pretty substantial European section.
North America falls in a similar category as Europe, although even more varied; it makes a lot of sense, considering how much more biodiversity you can find in this region. Sea lion, alligator, cougar, armadillo, lots of common zoo animals that are very popular even outside of America. There may still be a couple of holes in the animal selection (namely the American Black Bear), but overall we've got all the animals it takes to make a great North America section.
And now we get to the big ones.
Africa of course got the most animals, and it makes sense considering how many common zoo animals originate from Africa. It basically got two dedicated packs (Africa and Arid), with other additions in basically every non-regional pack, minus aquatic. The grassland and desert part of Africa is definitely very fleshed-out, with dozens of animals available.
Tropical Africa, however, got a limited number of additions over the years, and it's still carried by its base-game animals (which, to be honest, make up a very good selection)... The only thing missing now is some kind of smaller monkey, perhaps a guenon.
Madagascar also got enough animals to create your average Malagasy section, which usually means a couple lemurs and fossa.
Similarly to Africa, Asian animals are also easy to find in any non-regional pack. In addition to that, while "Asia" as a whole never got its own DLC, we got packs for Southeast Asia, Eurasia, and now what looks like India/South Asia.
As of now, Southeast Asia and Central Asia have some of the best representation in the game, with well-balanced and varied rosters, and while South Asia has a few holes they will hopefully be filled by the upcoming pack. Even the Middle East has a few animals, although most if not all of them are shared with Africa.
The only region that may still be missing a couple animals is East Asia, with several people advocating for species like the raccoon dog and other Chinese/Japanese animals.
And now, the big issue everyone is aware of: South America.
While every other continent got its fair share of animals, including Europe and a few specific regions of Asia and Africa, the most biodiverse continent in the world got repeatedly shoved under the bus - even in what was supposed to be a dedicated pack. On paper, South America has 46 species in-game... But in reality, if we exclude all the nonnative domestics and exhibit animals, we end up with a mere 20something habitat animals. Applying the same treatment to Europe, we get approximately 18 animals.
The thing that's really frustrating about this roster, aside from the limited number of animals, is the actual choice of species itself: two of these very limited animals are domestic camelids, two are caimans, and most of the other animals aren't even exclusive to South America, but rather shared with North America (noteworthy examples include the peccary, armadillo, flamingo, and cougar). As a result of this, we can't really make a South American area that really stands out, because it's going to be either filled to the brim with the exact same things that are already in a North American section, or incredibly empty, with only the few "big ticket animals" and not much else.
After nearly six years, it's almost unbelievable that we only have two monkeys from the region - one of which was added this year. The Americas Pack that we all waited so long for gave a small boost to the roster, but didn't fully commit to fixing the problem and instead gave us the Bighorn and coyote (which I actually love, but not as much as a coati or mara).