It doesn't really matter what they call it, does it? Just like changing the name to "main" didn't achieve anything.
Words have multiple definitions. The definition that git's usage is based on is:
an original movie, recording, or document from which copies can be made. "the master tape" synonyms: original, archetype, prototype
This shouldn't have been "problematic" either way. It's just all virtue signals. We aren't rushing to rename Master Degrees are we?