the folders shouldn't need to be zipped, but it is a bit worrying that they aren't coming zipped
are your screenshots going to the correct place? it could be the mac issue where it's looking at the root directory instead of blockland's directory
I had an issue back where I got a new computer(This mac)where Blockland wouldn't load off of Steam, so I looked at the Steam forums, and what I ended up having to do is going to Steam/steamapps/common/Blockland and deleting the app there, and re-downloading the demo version of it, and replacing it with the deleted Blockland.
Here are some screenshots of the inside of my Blockland folder, compressed and regular addons, inside of an addon, and how it comes downloaded.