I agree. I'm not saying it is. To be clear, I still really enjoy building a lot. But when a challenge isn't running, I find myself pausing the game just to build and therefore not really playing the animals as much. Or I have so many ideas I lose motivation because I'm not sure which one to pick. Having the challenges gives me something to channel my energy to. It rounds out the rest of my playing style so I don't get myself into a rut. I'm not saying the game is boring, just that I enjoy having something else to look forward to. When I can't do that challenge or don't want to, I ignore it and do my own thing. I have sandbox games for my building zoos. Franchise is for when I want to play with other players (So to speak) and have outside influences.Planet zoo is/has so much more than just community challenges.
I was mainly saying it's hard to get excited (like I was before) and rush home to play it, because now, I have all the time in the world. There's less motivation when there's no icing, even if you still get the cake.
There are alternatives of course, like The Round Table website has a community challenge operation for ZT2. Or they could add in more difficult objectives for the zoo objectives. Or I can do like I am and just make single goals, like breed X number of this species and release X females. I just liked the feeling of community where I wasn't actually playing alone (even though I still was)