That is a great question.
One of the very first things I wrote was not YA. It was a semi-creative-narrative thing where I took too-personal elements from my life and tried to write about them. Didn't work out well and ended up in a recycle bin in a galaxy far, far away :-)
The next thing I wrote was an erotica that involved characters age 18 an above. There was no NA - New Adult - distinction at the time so it was what I called a suspense romantica. Pen name Rayven Godchild so I could actually "debut" at a later time with my own name tied to a later work.
When Lord of the Rings hit the scene with a splash, I got the courage to finally act on a story idea that had been brewing in my mind for a while. I created a new world with magic, governmental hierarchy, sound-based ancient language based on our 26 letter system, legends...the works. Even involved a bit of necromancy. But my Searchers of the Unicorn Horns series hasn't had a chance to see much light. It was definitely YA.
My works, since this idea, have all been YA. And all have involved fantasy/sci-fi. Around the blogosphere, there are lots and lots of writers, many of them YA writers/authors. I can't help wondering if there was some one thing that has so many of us out here as YA writers? Was there a particular catalyst that changed the dynamic or has it always been this way and I didn't notice it until I joined the YA writer ranks?
What are your thoughts