Wildlife conservation doesn't only extend to endangered species. It's about protecting ecosystems and ensuring the future of species that might become endangered in the future or that are important to the ecosystem where other, more endangered species exist. Porcupines and meerkats for example are widespread in their native ranges, but for zoos they are kept because a) they represent aspects of the ecosystem that are important but often overlooked and b) despite not being excessively poached or hunted, they are still at risk of eventual extinction due to factors such as climate change. They are also easily accessible to zoos, which is another reason, but I digress.
I totally disagree that domestics have no place in a zoo game. As has been repeatedly said, by me and others, even in the context of not being happy about this DLC, zoos contain domestic species; some even play an active role in what is called rare breed conservation, i.e. protecting specific breeds that aren't common anymore due to being replaced by breeds that are more fit for purpose (none of the animals in this pack fit that description, obviously, but anyway). So a barnyard DLC makes sense, whatever, that's not really the issue in and of itself.
I 100% agree that Earth Day was the wrong time for this. One might argue that there is no "right time" for a barnyard DLC, but I think a lot of comments have suggested otherwise; a recurring thought here is that if we really thought there was more DLC coming, then this would be far more palatable. So there might not be an "ideal time", but there is certainly a "wrong time".
This is a period of uncertainty. Everyone had high expectations for this pack. No matter which way you look at it, the timing was bad.