Just because it is not working for you, does not mean it is a bug - this game is a lot more complex and unforgiving than some people expect, 90% of the 'bugs' I have helped people with are actually user error.
I've been wondering about this...but most of the time it seems like people aren't posting enough information to figure out if there's a problem in the zoo or with the game. The game is really opaque about the "rules" of the management side of the game, and I think that the real reason so many people are getting so frustrated with the game. Even when someone posts that they "suddenly" are having issues, I have this sneaking suspicion that many did change something, but didn't realize the impact it would have, or the zoo hit a guest/animal/employee threshold and an underlying issue that wasn't an issue before, but now is.
My first franchise I set up as a breeder zoo, and for the longest time I put no shops in at all. It got to a size, and I finally caved and added a small food court. It was immediately mobbed, I got tons of trash, the zoo was completely unable to deal with it, and it started to tank. Unhappy people, vandalism, pandemonium. I ended up deleting the food court, but by that time I had the starting CC I wanted, so I let my animals live out their lives, and effectively closed the zoo.
I've been very careful and organized about how I layout my current zoo (Peneberry Park, I put up a reddit post a week ago if you want to see), and I haven't had any of the problems that other people have been describing. I've got a couple habitats that are riding the edge (I get a notification about cleanliness, but when I go to call the keeper, that keeper is already in the habitat finishing the feeding, and gets to the cleaning directly), but other than that I've had very few issues with keepers, caretakers, mechanics, and refunds.
I'm having some frustrations with vendors right now, but it feels more like I just don't have the management and staff hut placement worked out correctly more than I think it's a bug. I could probably fix it, but I'm somewhere between I can't be bothered and I'd have to do some broader structural changes to the zoo to actually fix it.
This probably belongs in a different thread, but I've also had cause to wonder in my current zoo if the guests have a similar but different and hidden "novelty" stat. Guests will swarm whenever there's a new animal in the zoo, and it seems like if you don't add a new habitat for a long enough time attendance starts to drop. This happened to me in my current zoo when I was transitioning between the habitats I built to start the zoo and starting building up the way I actually wanted the zoo to look. I was doing a lot of building and terrain modification but not adding any animals. I started losing money, and had to scramble a little to get back in the green.