Promotion to Supreme Unity could indeed be kept secret, provided it was shielded by Hong Jun within the Purple Haze Palace, or if the Monster Clan Remnant used special means to conceal it.
Devil Bull King was associated with neither, his origins were clear, recognized as the new leader of the Demon Race after the Fated Calamity. With a transparent background, everyone felt he was the dark influence of Tushita Palace.
As a result, when Tushita Palace was yet to take action, the moment the phenomena of Devil Bull King's promotion to Supreme Unity arose, countless Great Powers turned their attention here.
Then, everyone grew restless.
Devil Bull King wasn't some minor character.
And after his promotion to Supreme Unity, he was even less so.
