The point is - 'freedom'

Maybe because people are discussing an operating system rather than an ethic which some hold to be the most important thing, and others less so?

> when referring to an operating system creates an uncertainty.

It's not an uncertainty that really has any practical effect. For example, I'm unsure whether GNU/Linux refers to a system running sysvinit, upstart, or systemd? Does it run X or not? What about GNOME, KDE, other (GNUstep)?

If people are referring to Android, they're pretty good at calling it Android. The people running uclibc and other exotic userlands are such a niche that it is not in any way a useful distinction to go out of your way to make.

Note here when I say 'useful distinction', I mean in purely technical terms; it's apparently a useful distinction for an organisation seeking to hang on to their relevance by piggybacking on the work of others who do not necessarily share their goals.