Why can I not make a hard link to PkgInfo?
This is an undocumented security "feature" of macOS. See https://groups.google.com/a/continuum.io/forum/#!topic/anaconda/CB0zClGfh3c


  This turns out to be an issue specific to *.app/Contents/PkgInfo and .app/Contents/Resources/.lproj files. OS X does not want to permit the creation of a hard link between one of these items in an application bundle to another file in a non-application-bundle folder. I was unable to find an explanation for this behavior in Apple's documentation, nor in the source code for HFS or the OS X kernel.