Because it's probably going to get leaked like the last CityRPG
Add-Ons usually only get leaked when the owner is careless about who the code is shared with. And since Brian and I are the only ones currently in possession of the mod, and we plan on it staying that way, I dont really ever see this mod being leaked.
The main reason, among other reasons, that we want to keep this mod private is because when an Add-On is overused and widely accessible so that anyone can host it, it no longer becomes special, unique, and fun.
*cough* CityRPG *cough*