This Grand Elder Hong Yun was a brilliant prodigy; the kind that had not been seen for tens of thousands of years. Through his painstaking research of the Tian Peng Transformation, he was able to incorporate many more true spirit transformations into this technique, thereby creating the 12 Awakening Transformations.
Unfortunately, even as a Body Integration Stage being and sourcing many types of true spirit bloods over many years, he was only able to invent 12 transformations. After that, his spiritual sense and physical body were no longer able to cope with the demands placed on them, thereby resulting in him being driven insane and killed by backlash from the true spirit bloods.
Back when this Hong Yun was the grand elder, the Tian Peng race had been at the very height of its power. He was able to ascend to the position of grand elder after inventing this cultivation art with his brilliant aptitude, thereby allowing him to rule over the entire Tian Peng Race. As such, not only was this cultivation art the key to his success, it also became his best-kept secret, and he didn't reveal any of it to anyone else.
All of the other elders at the time only knew that Hong Yun had invented a cultivation art known as the Awakening Arts, but they knew nothing else about it.
After that, Hong Yun was driven insane due to true spirit blood backlash and passed away, so the contents of his Awakening Arts remained a mystery.