First they completely leave him out of the Shurima event (even though he is born there) while including Ezreal (who just got his gauntlet from there). Then, they go and give his Fnatic skin away to Karthus, who Xpeke is known for being bad at.
Did they just forget Malzahar still exist or what?
Yes.
Probably because they don't want to highlight other champions repeatedly. When the void event comes around, Malzahar will be very important to it, and having him also in Shurima cheapens that.
they see him as a icathian... not a shurimian.
They've updated his voidling AI and given him a couple other QoL changes relatively recently (well within a year), and he can't really connect with Shurima. Ezreal can get away with it because of his amulet, but Shurima was before Malz's time. As for him not getting a Fnatic skin, I think the players themselves might have some sort of input on that, though I'm not sure.
