I don't really understand criticising people for what they want in the game. Some people love the game in its current state and just want some engine work, aviaries, reworks to systems like pathing, terrain, exhibits, and don't really care about species improvements for the majority of species in game... with that logic, of course it would be a shame to not have all animals in base game given they would just be ports.
For people who want to see improvements to animal designs, animations, more developmental stages from babies to juveniles etc, improved terrain and climbing interactions/animations, so on and so on, it makes sense that they'd accept a lot less animals at a lot higher quality, with the potential of more returning through DLC.
The fear of the first group of people is that (some of) their favourite animal(s) currently in PZ1 would be omitted from PZ2 with no guarantee of return. A legitimate fear that has happened in many different games from Zoo Tycoon to Pokemon. The fear of the second group is that some of the current jank would not be addressed in a sequel with no guarantee it would ever be fixed. Now, in all likelihood the second group of people will end up getting what they want, but it's totally fair to have the viewpoint of the first.
Let's not be getting mad at people for having a different mindset when all they want is to play a game they enjoy