Because the aardvark entered the English language much later than the other Germanic animals it didn’t acquire a proper pronunciation yet, saying termiet when it means termite, nacht instead of night, and graaf when it means grave, which it never does, for it always means dig.
After three centuries of ridicule it has got fed up with its name, its fame and its tongue (which is rather longue) and these days will only respond when addressed as Orycteropus afer.