I mean, if you want to realistically think about walkthroughs ... you need to think about several things:
How physically durable and temperamentally calm is the animal? Like if a toddler yanked on the animal's ear, would it be injured (as would be the case for many smaller animals), is it more likely to jerk away and run or strike out (most walkthrough and domestic animals are not predators - their first response to stress is to retreat). The more naturally social an animal is, the more likely it'll have some less dangerous behaviors to resolve stress (not in all cases but still). Can the animal withstand a kid throwing a small rock at them, pulling on an ear, pushing or grabbing them, an instagrammer trying to climb or drape themselves over the animal, or pick it up? There are usually keepers everywhere but they don't always catch a problem in time - the animal has to be able to withstand the human tendency to be stupid.
How likely is it that an animal's aggressive response will hurt someone? Sure, domestic goats can butt but the vast majority of the time, that just knocks someone over and bruises them. A badger's defensive response involves sharp teeth, same for a red panda. The idea that a giant anteater is a walkthrough animal is flabbergasting to me - the disembowl predators with those claws.
How endangered is the animal? Zoos aren't going to interfere with an animal's potential to mate/be released into the wild by wasting their time in a walkthrough. Even for the most domestic and calm animal the crowds and disruption of walk-throughs are stressful. Endangered animals tend to be shy anyway - they'd never breed under those circumstances.
How likely is that illnesses can transmit between the species and humans? Thus, zoos avoid exposing primates to human contact - it's one reason you'll often see glass walls between guests and primates - protection for the animals against snotty humans and vice versa. As we see more and more transmission between humans and animals, I expect we'll see more and more restrictions in interaction.
Some animals have such a long history of human interaction in zoos that they continue even though it's not smart: flamingos - generally too fragile but while you can walk through their exhibit, they tend to stay well out of reach. Zebras - other semi-wild equines, stupid idea but we're so used to it. Used to be you could feed elephants but ... well, that was a dumb idea and I don't think anyone does it anymore.
Most reputable walk-throughs use domestic animals only: they can hurt you but are so human adapted that they generally won't. So, the domestic camel should be a walk through, like the llama, for example.
...
