I'll try my best to phrase this delicately, as I understand it's an emotional topic for Americans right now, but perhaps RBG chose not to step down because she knew that the action of stepping down was inherently political, and after years on the court, had decided to avoid setting a precedent of Blue/Red judges tactically stepping down when their respective party is in power.
Who knows what her real reasoning may have been, but that's my interpretation.
Who knows what her real reasoning may have been, but that's my interpretation.