It has been a long debated topic whether or not hybrids should be allowed within planet zoo. I think it would be a fun easter egg for them to add into the game and people can choose whether or not they want to breed them. (Think of the killer penguin in zoo tycoon 2... People had a choice whether or not they wanted to exhibit them. Many people found that animals existence in the game fun.)
I see it a lot where people seem to use the argument that a zoo's goal should be conservation, however that seems seems to go out of the window in Planet Zoo when it comes to breeding leucistic or albino animals. There is a whole economy on the game centred around the selective breeding and distribution of variants not commonly present in wild populations. It'd seem like madness for people to advocate for the removal of content or diversity in the game even if these exterior traits and bloodlines are often products of successive generations of selective breeding (primary produced in real life in order to bring in more guests to see the rare or unusual animal colour variants).
Regardless of your personal beliefs, hybrid animals do exist and are showcased in zoo collections around the world. There are zoos and wildlife parks within the US such as Sierra Safari Zoo, Garold Wayne Zoo and the Myrtle Beach Safari Park, which exhibit Ligers for instance. Those are just a few examples in the US. Within Australia, Canberra Zoo possesses a Tigon in their collection. There are also Zoos outside of English speaking countries such as Bloemfontein Zoo in South Africa, Novosibirsk Zoo in Russia and the Hainan Tropical Wildlife Park & Botanical Garden in China, which produces Ligers and other big cat hybrids. These hybrid animals are impressive and intentionally produced to bring in guests for funding or educational purposes. Even if there are legal constraints in place in English speaking countries, that doesn't mean that the entire world will follow those same rules. Planet Zoo isn't targeted towards people living in a single country, it's a globally popular game, where people can build their zoo in any part of the world they wish.
Planet Zoo involves creating a zoo. There are no rules to how you make your zoo. You are the creator. You can setup a zoo in any country, and follow any ethical regulations you wish. One player may inbreed their animals without concern of genetic diversity. Another player might be strictly against the keeping of albinos and put them down when they are born. Another might breed gharials and not want to raise the bad stat babies so feeds them to saltwater crocodiles. Another may adopt critically endangered animals for their enclosures but never attempt to breed or release any to the wild. Those are just some examples. Not all players follow the same ethical considerations in their video games as you might.
If you don't like hybrid animals that's fine, but it's not right to say that all zoos are targeted towards the same goals. Many are run primarily as businesses, whether they try and paint it as ethical or targeted towards conservation or not. Hybrid animals do exist and would be popular in Planet Zoo as people love freedom and the ability to make their own choices and decisions. The sheer popularity of albino animals in this game highlights the communities love of rare, unusual or interesting animals. A zoo can still possess hybrid animals in their collection and also focus on conversation / education. Hybrid animals are not oil and conservation isn't water, the two can be mixed. Just because a zoo produces a liger, doesn't mean it can't continue to breed purebred lions or tigers.