Why is dragon a type?

Dragons are not beasts or monstrosities. Why do they have their own type? What makes their essence unique? Why are reptilian monsters like basilisks, behirs, chimeras, cockatrices, hydras, etc not considered dragons?

Dragons are reptilian personifications of the winds of magic. They come in countless forms and behaviors. Some are intelligent and delight in collecting treasure and holding princesses captive in opulent castles. Some are wise and serene, protecting sacred place until adventurers seek them out. Some are bestial, barely distinguishable from mortal animals. Their exact properties depend on which combination of the winds composes them.

Where do dragons come from? How are they born? How do they die? There are many answers to thees questions. All dragons are fundamentally personifications of the winds of magic, much as elementals personify the natural world. How they enter existence, and how they exit existence, is highly variable.

Many dragons form spontaneously as a result of natural disasters or great outpourings of emotion. Others are born from eggs, formed spontaneously or laid by another. Sometimes hated misers or starcrossed lovers will be reincarnated as dragons after death. Sometimes any vaguely reptilian creature such as a basilisk, chimera, naga or even a kobold may ascend and become a dragon. There are endless ways for dragons to be born.

Dragons are dragons, regardless of body plan.

While dragons are traditionally divided into specific breeds with specific forms, such as western and eastern, this is a falsehood. Stories of sea serpents, shenlongs, linnorms, etc are a result of adventurers misinterpreting a given dragon's preferred form as indications of a separate species. Dragons are shapeshifters and may assume any aesthetic they choose, commonly due to their upbringing or environment. For example, chromatic dragons often assume the western aesthetic and metallic dragons the eastern.

Dragon-kin (Optional Rule): As a throwback to the Rules Cyclopedia, the GM might decide appropriate reptilian monsters of the monstrosity type are typed as dragon in addition to or instead of monstrosity. For example, the basilisk, behir, chimera, cockatrice, hydra, naga, and tarrasque. This shouldn't have any effect on game balance.