It's somewhat of a misconception, and a crossing of borders in audience as well.
Those you've listed all fall into the bounds of Young Adult books - the target audience are teenagers and/or casual readers. The only possible exception are the latter Harry Potter books (but that is by deliberate design).
All these stories are 'coming of age' stories, and are designed to resonate with their intended audiences (often teenagers). Having the main, focal characters be teenagers automatically allows the vast majority of the intended audience to draw a connection with the story. They are mostly about the growth of the character and them discovering who they really are, something most teens (and young adults) resonate with.
The Inheritance Cycle and Twilight are also very simple books. Very simple concepts, no real depth and really, really simple writing. There's nothing challenging or confronting in them, they don't ask questions of the author and frankly aren't that memorable. They were successful because they were well marketed and written to a predictable formula and the popularity only really took off when movies where made of them. They were also relatively short-lived phenomena (anecdotally, I don't know anyone personally who finished reading the Inheritance Cycle - I personally lost interest partway through the third book). The same can be said of The Hunger Games and Mazerunner They are quick reads where you don't have to invest a great deal of time, effort or thought.
They are, in short, popular because they sell. They sell because they are marketable and they're marketable because they're light, easy reads that have no real depth but just enough sprinkling to make them "edgy" but not controversial. They are also aimed at and developed for a specific target market and the success is often dependent on feature films and associated merchandising.
Stephen King has this to say about them, and I think he sums it up quite well:
"I read Twilight and didn't feel any urge to go on with her. I read The Hunger Games and didn't feel an urge to go on. It's not unlike [my novel] The Running Man, which is about a game where people are actually killed and people are watching: a satire on reality TV. I read Fifty Shades of Grey and felt no urge to go on. They call it mommy porn, but it's not really mommy porn. It is highly charged, sexually driven fiction for women who are, say, between 18 and 25."
Harry Potter, and is a somewhat different beast and done so by deliberate design. The story grew up as the character and the audience grew up. It's still a coming of age story, but there is a depth to the latter books that simply doesn't exist in the other series. Many comparisons have also been made regarding the abilities and motivations of the authors themselves, but that's getting wildly off-topic.
In short though, the "Popular" Fantasy novels (that is to say the main-stream media reported ones at any rate) feature Teens because they are Teen/YA Stories.
As for Fantasy itself - that depends entirely on the story itself, and as many examples you can provide where teens are the focus, there are many, many more where they aren't:
Steven Errikson's and Ian C Esslemonts Malazan books (and all their offshoots) certainly don't.
Brandon Sanderson's Stormlight Archive
David Gemmell's Drenai series
Steven King's Dark Tower
Scott Lynch's Gentleman Bastards series
Brian McClellan's Powder Mage trilogy
The list goes on