Xerath's didn't match his identity at all. Not only that, but it made him harder to deal with when ahead, and was effectively useless when behind.
Jax became an effective tank because of his passive+ult and all the other free stats he had, despite building glass, meant he could pretty much kill anything late game. That passive made it so he had literally everything outside of range going for him after he grabbed gunblade.
Kayle's original passive just simply wasn't healthy with her kit. There wasn't any gameplay around it. You just stat-check someone's defenses while you didn't have to worry about what stats you have outside of offense because of her ult.
Vlad is effectively an AP juggernaut. He's extremely short-ranged for a mage, has no CC, has no mobility, but has a lot of damage and health. His passive is all that allows him to be that. Why would Riot even think about removing it unless they wanted to make all of his abilities scale on HP, essentially recreating what they just recently tried to nerf out of existence?