How do I know? Well, first, I take my head out of the internet BS for a day and go to a bookstore. Or even the library. Look at what's on the shelf.
YA is split almost evenly between fantasy/sci-fi and contemp.
So why does contemp get so little attention compared to fantasy? My guess is because fantasy is more like candy, and the internet loves candy. So does the film industry.
Fantasy has more eye-catching book covers. Fantasy has more high concept plots.
But if you also watch the daily publishing deals-- books that are being sold to editors now; they aren't on the shelves yet-- you'll see that contemp is still selling. A lot. More than dystopian, or steampunk, or any other branch of sci-fi.
Yet those sub-genres are getting buckets of attention dumped on them almost as much as fantasy is, and I believe the reasons for this are the same as I mentioned above for fantasy.
I agree that fantasy and sci-fi are entertaining reads and play an important role in getting teens to read more, but there are real teens out there dealing with real problems, and that's where contemp steps in.
If a sixteen y/o girl goes to her school counselor seeking advice, do you think he/she is going to suggest reading about ghosts, vampires, werewolves, or fairies? Not likely.
(Aside: I am in no way bashing sci-fi & fantasy here. I read it. I write it. I am even published in it. Lydia = not a hater.)
Yes, there are core life lessons at the heart of even the most fantastical stories, but when you need to be blatantly obvious about something, you need clarity that is only found in a real world setting with realistic characters. Stuff you would encounter in your average "day in the life of [fill in the blank]."
How often are rape issues addressed in fantasy and sci-fi? Quite a bit, actually. Yet what is the first book you think of when you see the word rape? Is it not Speak by Laurie Halse Anderson?
Why? Because it presents a situation a girl could find herself in right here, right now. When a girl reads that book she doesn't have to stretch her imagination too far to see herself in those shoes. She can easily connect. The point is made, without any distracting fluff. Books like Speak have the ability to help teens with real issues they are facing in the real world. Today.
If they can't get through today, they might not feel tomorrow is worth seeing.
And there is more than just rape to deal with. There are family issues-- divorce, sibling rivalry, parental abandonment, etc. There are drug issues. There are death and grieving issues. There are thoughts of suicide issues. There are mental health issues. There are bullying issues. There are academic achievement issues. There are monetary issues. There are finding your place in the world/ discovering your purpose issues. Their are religious issues, and questioning of faith. There are self-esteem issues. And on and on and on...
Any one of these things can feel overwhelmingly huge when you're a teenager. It can feel like you're trapped beneath it. Pinned, arms flailing, with no hand reaching out to help you escape.
This is why, as a writer of YA contemp, I don't worry about the YA contemp market supposedly dying. Not one bit. And I hate seeing this questioned every time a group of aspiring YA authors gets together. It's equivalent to wedging a shard of glass under my fingernail. Just think about it for a minute before you open your mouth (and maybe even do some simple research, like walking into a bookstore and actually looking at every title in the YA section). As long as there are real teens living in the real world, there will always be a need for these types of stories.