A combination of people forgetting how to play against a heimer, and the fact that some of the new champs are hurt more by him than older champs. Such as Elise, who has two skillshots to be cockblocked by turrets and a gap closer that is predictable enough to land a stun grenade on her, while also killing all her spiderlings.
Because he isn't just inherently weak, if the other team doesn't know how to deal with him he will probably stomp his lane. Can poke out the enemy laner and while he can't escape ganks he has a great kit to turn around ganks if they aren't coordinated.
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