Maybe because Zed and Talon for example are not the best team oriented picks in this meta? Ofc that a good Zed will probably win the lane against Veigar but it doesn't mean that Veigar wont manage to get to the late game and to the point where he's actually extremely useful for his team, and there's literally no assassin in this game whos more useful for his team than the late game mage.
And don't say: "If you are Zed, finish the game before 20 min mark" because that point is valid only in bronze and silver elo games.
Yes, I am playing a lot of Zed and assassins overall and I am not QQing about Veigar, he is fine imo but even if I manage to 3/0 him during the laning phase and snowball myself, when the late game comes, Veigar becomes a monster who's like 10 times more useful than me in literally everything.
He's similar to Nasus, there are a lot better top laners than Doge but once Doge get's 400+ stacks there's no top laner that can match him :D :D