> Asimov did write female characters but they are rare

To be fair, Asimov didn't really tend to write very character-focussed fiction much, his male characters were generally no more developed than the female characters; protagonists were mostly lenses through which to explore the tapestry of broader systems, while non-viewpoint characters were mostly low-detail elements of the scene, he was more interested in showing the forest than lavishing detail on individual trees.