Because he is hella easy, there is no denying that.
He can basically let his jungler auto snowball by flash ulting ontop of someone.
And if he´s half decent he can just avoid skillshots, push lane and avoid interraction as much as possible while not dying.
And punish mistakes from any more difficult mage fairly easily.
However when it comes to truly skillfull players they can easily punish him and his passive that basically stay down permanently as long as you harass him.
So when a meta sheep that happens to go midlane and picks ori or Syndra because "Omg mage OP" happens to encounter a malzahar while essentially having 0/very little practice on their champ......then the malz, even if he is similarly a metasheep with 0 practice will usually win by default.
Because easier champ that lets jungle snowball.
I played malz since before his rework, i played it after until now.
And ori is definitely the champ i struggle the most with when its a good one x) I can run over fizz like he doesn't exist and i can stall against Xerath or Azir.
But ori wrecks me in lane and that's hard to deal with, playing against a good one and you´ll barely have farm and your passive will be down near permanently unless you choose to run away to let it regen.
While missing all the CS in the meanwhile.
Not to mention, the expert ones have proven a tendency to time their ults to disrupt mine unless i flash ontop of them to avoid it.
No malz main will ever tell you that you can disrespect an Ori in lane and get away with it.