Not sure I agree with Anthony McGowan when he says, “Some of these books appeal to me, as an adult, because they are not teenage books at all.”
He seems to be discounting the possibility that teenage or YA fiction is capable of also satisfying an adult reader.
Just because I, an adult, enjoy reading a particular YA novel, doesn’t make it any less YA.
I’m currently reading RADIO SILENCE by Alice Oseman, a novel deeply embedded in teen experience and culture. It’s very clearly not a book that would have been suited to a publisher’s adult fiction list, but that doesn’t prevent it being a good adult as well as a good teen read.

So what’s the problem? Well, I’d contend that at least some of these books appeal to me, as an adult, because they are not teenage books at all. They are adult fiction. The themes, the style, often even the characters belong in the world of adult literature. It is just some quirk of publishing that has left them washed up on the YA shore. For example, Mal Peet’s masterpiece, Life: An Exploded Diagram, was simply the best novel I read in 2011. It should have been up for the Booker prize. It was published as YA because Mal had always been published as YA.

Alongside these many fine novels there is plenty of dross. As with most areas of publishing, YA follows the 90% rule. And much YA is a lazy, disheartening mush of false problems, fake solutions, idealised romance, second-rate fantasy, tired dystopias. Easy to read; easy to forget.

But my main concern isn’t with quality. For me, the problem is that a huge amount of theoretically teenage publishing is churning out books that simply aren’t for teenagers at all. And that must mean, given the finite opportunities for new books, that “real” teenage books aren’t getting published.

via Most YA fiction is grown-up fiction in disguise | Books | The Guardian.