I'm becoming increasingly convinced that the zoo limit was an intended feature.
Because this game is published by Microsoft, I feel like the most likely reason is to set things up to sell some DLC in the future.
There's a decent amount of animals in the game but there are even more out there that isn't. When it comes to micro-transaction games, it's a gold mine because you could possibly release a lot of individual species for a dollar each or whatever. Once more content is out, the limit is increased to allow players to add the new stuff. The "nice" part of that is that players don't need to tear down their exhibits to add the new stuff. Instead, they just add to their existing zoo.
Currently, it seems like they've provided a lot of existing content, too much land, and too low of a limit at the start. You don't want to cut down on content too much because you have to justify the $60 price tag but you also don't want to mess around too much with land and limits to make it easier for you to release content later.
If this is the case, then it's the tricky issue of finding the right balance. Personally, I think a mistake was made here in that the amount of visible land is too high and the limit too low. If they decreased the amount of available land by by giving you only half to a third and also increase the limit by 50% or more, there'd be less people complaining. Once more content is out, further increase the amount of land and limit.
In the meantime, I do hope that they (both developer and publisher) just increase the limit some more via small update even if there's no new content coming out anytime soon. The current balance is driving people away because most players feel like there's nothing to do once they hit the already low limit. It might not be a trivial change to make but if there's one thing I learned from this game, it's that you gotta do what it takes to get more customers and also to keep your current players, even if it means emptying all the trash cans yourself. If they ping customer happiness, they'll see what I'm talking about.
Anyway, I could be wrong but that's my current interpretation of things right now.