Why is Rengar the only stealth champion with a SFX that plays *while* he is stealthed?

He's the only one that gives clear visual and aural indicators that he's near, meaning that his ability to surprise-KO you is somewhat lessened, but he makes up for this by the tension and fear and, dare I say, the thrill that hunting his prey gives both players.

Then we have Eve who has her VFX that tells her when an enemy can see her - it's great for enabling stealth gameplay and the stealth mindset - but no SFX that could warn her prey. Imagine if she had 'night whispers' that got louder the nearer she was / longer she stayed around.

And Twitch - imagine if he could be heard talking to himself as he's approaching you: "Hehehe, they'll never see me coming!", "Like taking cheese from a dumpster, too easy, hehe...", or something.

Even Shaco gives off a puff of smoke and evil laugh when he disappears, but the laugh is really audible. You need to be standing right next to him with no other spell or ability SFX going on to be able to hear it. If it was audible within a large range, it would act as a brief telegraph to his burst - similar to the way Zed's ultimate has the delay as the three shadows dash in to Death Mark his target. It would open up his power budget since its more challenging to gank because of the SFX.

So what's the deal?