Someone with better freebsd knowledge should chime in, but until then... It is my understanding that the launchd port was one guys google summer project, he worked on it for the summer, put it aside for a couple years and picked it up recently.

The fbsd wiki on launchd: https://wiki.freebsd.org/launchd

Googling tells me that they have been working on porting it and apparently it is more or less done but not yet the default.