Because Itachi was supposed to be villain - not hero. Bad writing
The scary thing is, there are actually people who defend his stupidity and think he is a genius when he is obviously a complete retard
Itachi was a Good villain but Kishi turned him in a complete retard when pulled this bullshit that he was a good guy who only wanted to "protect his brother" through torturing and abusing Sasuke and slaughtered his family in front of him.
He mentally and emotionally tortured Sasuke yet expected him to turn out well adjusted. He intended to have him kill his friend, leading him to be a murderer and traitor, but expected this to turn him into a hero for Konoha.
it's obvious that itachi's entire character is only based on retcons.
Not to mention Itachi helped to kill six Jinchuuriki when he collaborated to extract their Bijuus to put in Gedo Mazo during akatsuki's reunions.
Itachi also has much more fault in Kazekage's death
He helped to Kill Gaara when his clone prevented the rescue Team to reach and rescue Gaara and save his life
Itachi become in a even worse criminal with his participation in Akatsuki.
This just turns the whole thing about "saint" and "hero" Itachi more laughable
Itachi is an international criminal, a member of the Akatsuki, he assisted Tobi in apprehending and extracting the Biju out of their Jinchuriki. He massacred the Uchiha in cold blood with no moral qualms, he probably also killed children and innocent bystanders who weren't involved in the Coup d'etat.
He's just like Danzo, they're both villains, they killed innocent lives and justified themselves for their ideals and selfish ends.
Itachi is just a piece of shit brother and despicable human being with no moral compasses.