“Why are there no libs installed?”:
The installers for most other operating systems have the option not to install the libraries. This could very well be the case for mac as well. (In linux the libs are separate packages and are therefore only downloaded if you want to install them. In windows you always download them as there is only one installer but you can select if you want to install them during the installation process.)
Another option is that you had version 4 installed in the past. If this is the case then your personal (global) library table will still point to your version 4 setup. To fix this you would either need to “install” v4 libs and set them up or set up the library table to point to the already installed v5 libs. More details see: I had KiCad 4 installed previosly. Now i updated to v5. Now i have some problems with the library setup
“How do i setup libraries?”
The environment variables are only half of the equation. (If you do not use 3d models then they are really not needed.) The real setup for which libs are used is made in library tables. These can use environment variables to make a setup portable. (This is the reason why to official library tables contain environment variables.)
More details see: Library management in KiCad version 5