Loda made him retarded unfortunately.
There is no excuse at all to be honest, other than shifting blame to the senile author.
Anyone with half a brain (which apparently yonkos don't have) would've seen him get pierced by a demon and held up in air, literally grow wings and fangs......would've realized that this dude was obviously forcibly corrupted and mind controlled.
There was no "betrayal" at all, clearly. Kaido's entire philosophy of "pirates always betray you" was just him being retarded.
Just for a minor consolation, Roger and Garp didn't realize it either, until they heard Rocks through VOAT. I guess they were retarded too lmao.
Massive Loda L. 0/10 writing.