I think people here in the forums underestimate how much the overall public likes carnivores.
In a reddit survey, people we're asked what type of animals they don't want to see more added to the game, with the types being hoofstock, primates, birds, carnivores, reptiles and other mammals. Carnivores was the second least voted category, with the difference of 1 vote against "other mammals".
That’s the thing about surveys, probably the best way to actually get that information is for Frontier to post it on their socials for everyone. Reddit, this Forum, Steam, all probably have their own micro niche PZ cultures that can change the votes from one way to another.
Like on this forum this dlc possibly being the last is generally accepted based on the information at hand. I posted something like that on Reddit and I started to get negative karma. Only very recently have I noticed that change. Same with something like the LadyDesigner doing a survey. While it shows some of the PZ community, it mostly focused on her community.
It’s also very likely, despite all the comments asking for them, birds, marine animals, and monkeys may truly be not that popular. We might be a very vocal minority. Now not being popular does not equal not worth putting in the game. But that may be some of Frontiers decision making, they can track the internal data of animal numbers.
Though what might make these groups less popular could also be due to the lack of options. Who knows, maybe if we had more monkeys, birds, and reptiles it might boost their numbers. I would also get bored if I built the same habitats for the same 11 birds and the same 3 monkeys (a generous 6 if we count the lemurs as close enough).