Generally when software relies on glibc or the Linux kernel it can be patched so that it works on the BSD's. In my time of porting to OS X for example I haven't had anyone not take my patch to fix a problem an upstream it with a "thanks!". This becomes more problematic with systemd, whereby we can't port systemd, and since the software depends on systemd (most likely for some reason or another the software developer thought it was a good idea) we can't easily replace/rip out those parts of the code and make it run on the BSD's.
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Generally when software relies on glibc or the Linux kernel it can be patched so that it works on the BSD's. In my time of porting to OS X for example I haven't had anyone not take my patch to fix a problem an upstream it with a "thanks!". This becomes more problematic with systemd, whereby we can't port systemd, and since the software depends on systemd (most likely for some reason or another the software developer thought it was a good idea) we can't easily replace/rip out those parts of the code and make it run on the BSD's.