To reiterate what has already been stated (or at least attempted), the point of bundling a standalone zip on Windows is so that users don't have to scour the Internet for ENIGMA's build dependencies. On all other operating systems, these dependencies can be installed from one place.
On GNU and BSD systems, you have access to a package manager on which one line of code can install all dependencies, a second line of code can obtain ENIGMA, and a third can obtain LGM. On these platforms, we will be (in the near future) distributing packages that do all of this for you via your package manager.
On Mac, the XCode installer comes with all ENIGMA's dependencies, as would be expected—the installer is in the "multiple gigabytes" size range.
So on Linux, we will be distributing packages sooner or later, but this package will be under a megabyte in size and will instruct the package manager on how to obtain all dependencies. On Apple, it's not legal for us to redistribute XCode, and tacky to try to use anything else, so we are sticking with the XCode install followed by regular checkout. On Windows, the installer's the best we can do until such a time as, eg, MinGW-get is operational, or we support codegen to some intermediate format (eg, LLVM or CIL). The latter is not scheduled to happen very promptly, and the former has been a rumor for years.