The context is that many people (and especially public repositories from US companies) started changing the name to ‘main’ out of a misguided inclusivity push that comes from a niche political theory that says even if words aren’t slurs (which obviously should be avoided), if a word has a meaning that could possibly be connected to anything that could possibly be in any way sensitive to anybody, then we need to protect people from seeing the word.

In this case, out of dozens of ways the word is used (others being like ‘masters degree’ or ones that pretty closely match Git’s usage like ‘master recording’ in music), one possible one is ‘slavemaster’, so some started to assert we have to protect people from possibly making the association.