Malz's passive doesn't block Illoai's E

Because it's not damage or CC. It would probably block the first instance of dmg from it.

Why would it?

Malz passive isn't this god like perma barrier(as much as I would like it to be)

There are so many thing it blocks, stop complaining about the few things it doesent.

One game I was facing a ziggs mid, and when I reached low health I retreated, while I was recalling, my passive regened, and it blocked his ult damage. This happened not once, but multiple times in a game, because the ziggs didn't know not to do that.

In another game I was out of position in a teamfight, my passive blocked the cc from a gnar ult and the damage from a jinx ult, all because my enemy wasted all their damage on me in that .25 seconds. So, be happy for what you have, and don't complain, before malz becomes

Illaoi's E on hit doesn't deal any slows, and Malzahar's passive reduces incoming damage by 90%. So technically, you should still get hit by her E anyway with that leftover 10% of damage you'll receive.