It wasn't necessarily deemed "offensive", simply that its roots in master/slave terminology (indirectly [0] in predecessor VCS Bitkeeper which did have a concept of "slave repositories" that git fortunately does not share) was not the best choice of words and given they have the option to somewhat easily change the default, because it was already a config flag, they could just easily change the default (as this changeset does).

[0] The developer that chose git's default did not intentionally choose the default because it was Bitkeeper's default/terminology, but the developer was a Bitkeeper user at that time and its subconscious influence in reusing terminology would have been strong.