What makes writing worth reading?

Something is worth reading when the reader can find the main message that was supposed to be learned at the end of the reading. It's really frustrating when I read an excerpt or a story and when I'm finished, I don't know what I was supposed to get out of it.
Personal preferences have a lot to do with what someone thinks is worth reading too. I personally hate when I get to the end of a story and it leaves me on a cliff-hanging note (unless I know a sequel is coming that will bring a more completed resolution to the story). I tend to steer away from non-fiction novels, but I could still say that it'd be worth reading one if I learned something "interesting" while reading.
This question brings me to ask why book publishers deny so many potential stories to be published? because if they don't like what an author writes, they think the rest of the world couldn't possibly enjoy it. If someone writes a book about a dream they had the night before and they bring a draft to a publisher who doesn't like it, who's to say that there's not someone out there somewhere who might get something out of it?