Because the project is not well-maintained and requires slight fixes to allow this library to actually be used.
I would generally suggest moving away from this repository. An alternative has been started by @felixjulianheitmann at licensecxx. This might me more suitable to use as a library. However, it's still under development.
License generator for licensecc allows to create new projects (and their public and private keys) and issue licenses.
It is a standalone project, but the code in here can be used as a (git) submodule of licensecc project,
so unless you don't have specific issues you should compile it from there.
All the documentation is in the main project.