Blood uses the build engine which was open sourced at about the same time as Quake, there are numerous source ports and it can run on most platforms (although people have gotten it running on mobile devices, there's never been an official port). As nblood is based on eduke32, I'd imagine the only reason it isn't available on more platforms is that no one has volunteered to do it.
The Build engine's source code isn't enough to port any game running on it, since Build was made as a library (I believe most developers using Build in the 90s didn't have access to the source code).
Also, wasn't there an official Blood port by Nightdive Studios?