I really think this misses the point. Nobody said Github was "trying to solve racism", nor that they believed their efforts should end with that move. And what they are doing did not, as you imply, come from nowhere. You just weren't paying attention to what they were paying attention to. There's been a movement for a number of years behind the deprecation of that word in contexts where "master" implies "slave", as this context does. It's happening in real estate as well, as an example. See also: backlog "grooming" becoming "refinement". The issue is that there can and will be instances where thoughtless use of a loaded term can make someone in the room uncomfortable. And if we can help avoid that, simply by shifting to a compatible term with less fraught history... why would we not?