Sylas's ult with kennen?

Sylas "Sylas steals the enemy's ultimate ability and can cast it freely"

Kennen "Kennen summons a storm that strikes at nearby enemy champions for magical damage"

i was facing a sylas just now and i do not get it.. How does it make sense when he steals my ult he also takes my "passive"? That makes no sense what so ever... Kennen's ult has nothing to do with his passive meaning with out the passive the stun wouldn't happen. i don't get it cause he doesn't take the passive plus ult of any other champions that i know of.. GO F YA SELVES WITH YA DOWN VOTING AHSES JUST ASKING A QUESTION U TOXIC FLIP FLOPS