Unfortunately, that's Aonuma's job. They developed PH and ST with Toon Link in mind because Aonuma loves him, even when the userbase clearly prefers something more dark like OoT or TP.

As long as he is in charge, we will keep getting Cartoon Zelda.

People are playing something else ... it's called Playstation and XBox, which overwhelmingly get chosen over Nintendo in large part because most people don't want a platform centered around cartoon franchises. It's unfortunately why you'll have a generation of kids who know what Skyrim is but not Legend of Zelda.

If so many people love "cartoon Link" so much maybe they should actually buy the games. Wind Waker sold waaaaaaay less than Ocarina of Time. Skyward Sword was laughably behind Twilight Princess. The new Triforce Heroes is also putting up dissapointing sales, maybe just maybe the audience doesn't want a cartoon boy Link?

It's not 1986 anymore. 

That was years ago. WW is well recieved now, and TP is universally looked at as a game that aged terribly. TP didn't sell more because it was realistic - it sold more because it was on two platforms, one of which was the massively successful Wii at the beginning of its massive fad.

WW is one of the worst selling 3D Zelda games. Together with its uglier cousin Skyward Sword. Metroid Prime 3 was on the massively succesful Wii, but didn't sell more than Prime 1... Userbase says little with core franchises like these.

And good for them. If they want something dark and realistic, and Nintendo aren't offering it, they should be playing on those platforms. Bravo for them. Zelda is too culturally relevant for it to fall out behind Skyrim, so that'll never happen. It's too iconic.

Again, if Nintendo needs realistic IP to get those guys, they need to make realistic IP, not change unrealistic IP. Each of those examples were purely circumstance. MM sold waaaaaaaaaay behind OoT with a much darker direction and the same art style. TP was marred by the regection of the Wii and motion as a platform by that time. ALBW sold great on the 3DS. People love cartoon boy Link. Had nothing to do with art styles. People who don't shouldn't be playing Zelda. Not in 1986. Not in 2015. Play Dark Souls. Play Bloodborne. Play the Witcher. Play Darksiders. Play something else.

Don't lie yourself with that. Soccer moms and grannies were not the one buying TP, those were us and some Xbox/PS fans. Why do you think realistic games are high praised in those environments? Because there's the demographic that play those games and part of that userbase is the one that bough games like TP.

Sometimes maybe you just need to listen to your audience. Batman once upon a time was this:

Which then became even campier/sillier

But the audience has overwhelmingly decreed that this is the Batman they prefer for the last several decades ... dark and serious

And when they went too silly with Batman again like the George Clooney version, the audience overwhelmingly rejected it

If DC/Warner kept trying to force feed a silly/campy Batman down the throats of audiences, the character would basically be a niche character that appeals to  small group of purists. Sometimes it's OK to listen to what the market is telling you, in fact it's vital if you want franchises to endure. For every Mickey Mouse there's a Popeye that has basically zero relevance to kids today because the character did not adapt to the times. 

And lets face it, Nintendo doesn't frankly have the gumption to make a dark/serious IP and invest real huge marketing dollars into it. Too risky for them and it would likely fail because they would have one "dark franchise" in a sea of cartoony fare. They needed to make more IP like that in N64/GCN/Wii days (or not lose them via selling Rare) when it was far less risky to make a new IP. With today's development costs, big time new IP like Destiny require a monstrous investment to get on the map. 

Zelda and Metroid are completely different IP-s. I agree that Metroid is supposed to be more dark and realistic, but not Zelda, Zelda always meant to be colorful fantasy world not dark and realistic. And no, majority of Zelda fans dont want dark and realistic Zelda, thats why Zelda U art style was very well received.

TP had great sales because was on two platforms and was launch title on Nintendo best selling console, Skyward Sword on other hand come out at end of life when basically Wii was dead and gathering dust in some corners, also required to buy addon if you want to play game.

No. TP sold well because the artstyle. Remember that TP was done with that purpose in mind after the "bad" reception of TWW style.

That add-on still sold enough to give the game a potential pool of customers almost as big as the install-base of the SNES, more than both the N64 and the GameCube. Plenty of people to sell to.