Well at the time of writing the Empire was in full collapse. And I think there was, and still is, this great question.
A rationalisation was that English society is made of better stuff, the volksgeist. These tropical places, the peoples, were naturally inclined towards chaos and violence. The male boarding school is perhaps the greatest symbol, almost a cultural idol, of this. Order. Class. Structure.
These institutions are temples of patriarchy. So yes using a female cast, perhaps from a comprehensive school, would be different. But I can easily imagine a group of girls scared witless by the Beast, and one stepping forward and saying, "Let's hunt it and kill it".