Quick question about Rengar's Ultimate

There's no need to be highly opinionated in a rude way toward's this question, I'm genuinely just curious. So I'm a Rengo main and there's always one thing that really bugs me which is his ult. When caught in a situation where I'm needed to ult to get away and I do, but happen to die before I go invisible and can actually use it, why is it that Rengar's ult doesn't get a small cooldown like Cait or Zed's ultimate? They get a small cooldown on it when they click ult on someone who died before it goes off, or if they die before it goes off. So why doesn't Rengar? (referring to getting the small cooldown if he dies before it goes off) He gets the full cooldown timer. :/