Robert Vaughan may not be a big-name author, but he sold tens of millions of books in the 20th century under many names. His pseudonyms include Paula Fairman, K. C. McKenna, Paula Moore, Fancy DeWitt, Patricia Matthews, Jonathon Scofield, Lee Davis Willoughby, and Kit Dalton. Have you read any Robert Vaughan romances?
While women comprise most of the Romance genre readership and the vast majority of writers, there are many men who enjoy the genre, too. In fact, in the early years of romance, there were quite a few male authors, who had to use pseudonyms to publish their works.
In the romance genre, an author might use an alias for various reasons. Perhaps their real name lacks a certain je ne sais quoi. Because some romance writers create fiction for multiple genres, different names ae used. Others are men who want to appeal to a vast female audience. Or they could be married couples or duos who need a catchy nom-de-plume.