The Immortals destined to meet calamity, or the multitude of mighty beings reincarnated for additional cultivation, their memories are usually awakened only upon becoming an Immortal or under specific circumstances.
Awakening too early may not be very beneficial to his current level of cultivation.
That is why Ye Ling would say such words, Donghuang Taiyi, after all, is a colossus in the Immortal Realm, his path of cultivation is unique and should not be meddled with lightly.
"Ah, Ye Ling, what do you mean by that? But I also feel, you know, that it seems we knew each other a long time ago."
"Heh, now that you mention it, I do feel quite a sense of familiarity, as if it has evoked some memories."
With a slight smile, Ye Ling said, "It's time for me to go. I will leave something for you. If you can remember something, that means you have reached this stage. If you can't remember, don't force it."