Few practice it because it has become so fragmented, nobody can say for sure what it is.
What if eight or ten different corporations were allowed to manufacture a product with slightly different specifications, but they were all allowed to call their various products by the same name?
It's conceivable that the "real" or original product could be killed off by a "new and improved" version by some other manufacturer. Or, as time passed, the original product, now being manufactured by third and fourth generations of management, could be slowly but inevitably modified and eventually turned into something completely unrecognizable to the original product developer.