I think that is an issue if you want to do realistic builds but a lot of the community don't care about that so it might not be a major part of their selection process (or a priority for the original poster). They may not be a 'random selection' but have other criteria including wanting to pick flora iconic to the region (even if they aren't used in zoos) or plants that increase the overall variety in the foliage types we have and are visually pleasing.
Not entirely sure about that, realistic and aesthetically pleasing builds are important for a great part of this community. The game thrives on the exceptionally built parks that are featured in social media platforms and so on, that is their major source of advertisement. The better and more realistic the zoo looks the more buzz it seems to generate. Now realistic has its own meaning in this forum and other places when it comes to this game, and not sure we are speaking about the same thing when I use it.
I will give you an example, the Baobab trees in the game are depicting fully mature trees that could be anywhere between 400 and 1000 years old, that is definitely not something you would find in a zoo, an African Safari or an excursion into Madagascar, definitely, not in a zoo. Add to that the bark coloration is completely off, and in no way representative of the real life texture of this trees. The majority of Baobabs you will find in zoos are replicas, some can be extremely realistic.
Another example the Kapok tree, now this is just an import from Planet Coaster, and a reason why the base game had very questionable foliage in comparison to the last two DLCs, Australia was amazing. Going back to the Kapok, the in game trees are representing mature specimens that have been sitting in some tropical rainforest for a few hundred years, that is again not something you will find in zoos.
Now if they are adding all of these trees, but also providing the amount of foliage that is required to built realistic zoos, I take no issue with that, because I understand that even though this game is called Planet Zoo, not Planet Africa, Planet Amazon or Planet Earth, there are definitely a variety of players here, and many do not even built zoos, they just built what they want to built and that is fine.
As an FYI, modern zoo landscape architecture specializes in getting flora that is exactly iconic to the region and more importantly the ecosystems where the animals exhibited are from. A number of times I will select plants for the visitor amenity areas that complement the exhibit that are not suitable to be displayed inside the animal habitats because they will get destroyed, but still merit being displayed in the exhibit given their iconic status. The opposite of what you probably thought I was recommending. Again we are speaking a different language here, and when I write realism, I'm covering a variety of angles and touching bases on a much broader concept than what you described.