I never really understood ‘young adult’ literature. I think it’s a rising genre because they muck up the teaching of reading now and we’ve got generations of teens who are poor readers. Just average kids who are taught correctly should be reading at a regular adult level by junior high—and then who wants to read watered-down pap?
You have no idea how many times I’ve heard, “but at least he/she is reading!”.
It’s always been a genre, tweens want stories about tweens, not little kids and not adults. It got huge when Harry Potter proved there were truckloads of cash in the market.