The philologist August Immanuel Bekker (1785-1871) compiled what became the standard edition of Aristotle’s text, and today every edition of Aristotle in every language uses “Bekker numbers,” the page numbers in this edition, to refer to pages in Aristotle’s text. As was common at the time, the language of scholarship was Latin. (Yes, this is the case even for Ancient Greek scholarship. You can easily find introductions to Ancient Greek texts in, say, the Oxford Classical Text series that are written in Latin.) This means that the title of the whole edition was the Corpus Aristotelicum even though the text is Greek. Each work was known by its Latin title: De Mundo, De Interpretatione, De Motu Animalium, etc. De Anima was no exception. The convention simply stuck around. Sometimes you’ll hear De Mundo in Latin too, and it is common to hear the same for De Interpretatione. Not so common for the Nicomachean Ethics or the Metaphysics, but this is the same as in Plato’s scholarship: sometimes, especially among older scholars, the Statesman is the Politicus and the Laws is the Leges. The convention is hard to die in some cases, but there’s no deep, philosophical reason why it sticks around.