After he became an Immortal Emperor, Yao Shi obtained a few pages with mantras from the Death Scripture, one the Nine Grand Heavenly Scriptures. He studied it and formed a new supreme dao. Since he already formed his dao and used it to shoulder the Heaven's Will, he couldn't use that new supreme dao. If he wanted to use it, then he had to start his Cultivation all over again. Because of this, Yao Shi chose to not create it and only left behind an outline for the Myriad Bones Throne, naming it Aphotic.