Cleopatra was the queen of Egypt, which was a vitally important part of the Mediterranean world during antiquity, especially due to its central importance to the grain trade and necessity for the dole at Rome. The interest of Julius Caesar and Marc Antony in her wasn't just a sexual infatuation, she was incredibly important geopolitical for securing Egypt. When Antony was fighting Parthia and later Octavian, Cleopatra was important in helping secure supplies, men, and the Eastern kings for Antony. During the Civil War Cleopatra also became a major focus of Octavian's propaganda as Antony was portrayed as being seduced away from Roman values, and his Roman wife (Octavian's sister) by the Eastern seductress Cleopatra. As that became the accepted version upon Octavian's victory, it would not have made sense for later historians to omit her from the story even if they had wanted to. Ultimately, her decision to leave at Actium when she did also helped to finally seal that battle and the war for Octavian. She is more than just a bystander to some of the most important historical events that took place at the time and worth writing about.

Beyond that, Cleopatra is a relatively interesting character for antiquity, especially for a woman. By all accounts she was remarkably multi-lingual, being the first Ptolemy to learn Egyptian for one, and very politically savvy. She was romantically linked to the two most powerful men in the world and was herself queen of a superpower, that's relatively captivating.