You are the moderator of your own community, I don't think its fair to expect the instance admins to moderate your community. They should only have to step in if your not doing your job. As far as this specific slur goes maybe its not on their radar, maybe they don't think the fight is worth it right now, or maybe they just give you the tooling to enforce your own level of uplifting environment. You can set the tone and expectations for your community however you like.