The size of an animal is absolutely relevant. If you're running a busy zoo, you need the ability to easily have a quick overview of everything with the heatmaps to make sure everything's okay. With smaller animals, this gets a lot harder to do and therefor makes them more of a gameplay-related liability than anything else. Even with lemurs and gazelles you can see those far more easily than meerkats or fennec foxes.
And as if the adults weren't hard enough to look for, good luck finding a rogue baby meerkat that got out of its enclosure. So either you have to pause around and put a full stop away from your bird's eye overview (which is unfeasible in Timed Scenarios that we get with these updates), or you go through a bunch of menus trying to get it resolved. Either way, there's no elegant resolution that lets you return to your quick bird's eye view, and therefore makes smaller animals and their babies very much not worth the hassle.
I get it, people have their favourites. But when you're making a game, you need to pick animals that work with the gameplay and not against it. If this means letting go of favourites, then so be it.