> I wonder if there's a compelling reason for these add-on distros (Fink, Homebrew, Macports) to be strictly "build from source" with no option for binary package downloads.
For that to happen, someone has to take responsibility for creating, managing, and distributing those binary packages. That's much easier said than done.
So, the simple answer is that no one has, as of yet, volunteered to do the work.