He published it w/o core package functionality. There are no plugins with KXC, that is one of their main arguments: don't rely on 3rd party code, bring it all inhouse, where it can be checked / maintained.
>UPSTREAM THEMSELVES decided not to include in default/recommended build instructions
This is false, or at the very least misleading. It doesn't take much to go on the repository and give a closer look instead of repeating "what other said". Kwpolska already wrote it in this thread, -DWITH_XC_ALL (the flag that's been turned OFF in the original Debian package rules) is explicitly called in the build instructions, and not only there but also one release tool [1] and snap config [2]. This is merely how the project manages its build configuration, with specific flags turned off and one master toggle enabled by default (or expected to be passed to cmake/bash release tool). Same thing for the ppa packaging. [3]
