Some distros could have configuration files in a directory different than /etc/. For example openSUSE switches to /usr/etc: UsrEtc packaging guideline
greetd has it hardcoded and only it
Would be nice to have options for building greetd that would take as a parameter vendor location and greetd first checks /etc/ and then vendor dir location for the config files.
it is not hardcoded, you can pass
-c/--configflag with path to config