All martial arts are human inventions, they are not products of divine revelation. They are developed by people through a process of experimentation, observation, and discovery, which is the same process that every student goes through to learn them. They are evolving constantly through adaptation and innovation, which is how they grow, spread, and differentiate.
Why are there so many different styles of martial arts? Because they are being created all of the time. Where do martial arts styles get their names? Sometimes they have descriptive names. Quite often they have family names – the family name of the person who developed and promoted them. Older does not mean better; neither, for that matter, does newer. All martial arts are both old and new. When you are learning a martial art, you are learning your teacher’s version of it, which is necessarily new, but your teacher’s version can only be a recombination and unique expression of principles that are ageless and timeless.
There is no such thing as a “pure” martial art, other than in a strictly relative sense. The oldest martial arts, like the dinosaurs, are fossilized in the mists of time, and only live on through their descendants. Every martial art is a derivation and distillation. They necessarily evolve as they are passed on, and no martial art exists in its original form.
Like open source software, martial arts are editable by anyone, at any time. There is no “best” one, but there is a variety of applications designed to meet a variety of needs, and they do vary in quality and usability. The question to ask about any school, teacher, or style is not “is this teaching pure/authentic/correct”, but rather “does this work for me”. Universal principles cannot be made proprietary. A good teacher will provide you with the source code, not a write-protected GUI.