Why are some champion passives so stacked?

Darius's passive gives his enemy's bleed, reduces their armored and at five stacks give him ad, Irelia's passive gives her attack speed per stack and bonus on hit damage at Max stacks, Akali's passive gives her extra attack damage and range, movement speed and restores energy, Yassuo's passive gives him double crit chance and a shield for moving, Sylas's passive gives him aoe attack on every ability and non of these have a cooldown, aatrox's is also stacked bit it has a cooldown at least. Compare that to champions like singed who's passive gives him movement speed near other champions and it has cooldown, or Xin zhao, who's passive gives extra attack damage and heals him on every THIRD attack or Garen's passive which just heals him if he doesn't take damage for a certain amount of time or Mundo's which just straight up heals him.