Here's why:
* Greek as the Language of the Elite: By the time Cleopatra ruled (51-30 BC), Greek had become the language of the ruling class and educated people in Egypt. This was due to the conquests of Alexander the Great and the subsequent Ptolemaic dynasty, which ruled Egypt for centuries.
* Official Language: Greek was the official language of administration, commerce, and diplomacy in Egypt.
* Cleopatra's Bilingualism: While Cleopatra certainly understood Egyptian, it's likely she primarily used Greek in her daily life and interactions with the ruling class.
It's worth noting that Egyptian, a language with a rich history and multiple dialects, was still spoken by the majority of the population during Cleopatra's reign. However, it was not the dominant language of power or administration.