I mean, TOS never mentions Sybok or Michael either.
Spock never mentioned Sybok because he was ashamed of him, and I'm coming around to the idea that Discovery and the Spore Drive may have never existed in the TOS original timeline. As to whether you want to put TNG/VOY/DS9 in the original TOS or this slightly altered version, I leave that as an exercise. Time is sticky, as we just learned, it's possible that they may be the same in both.