The majority of books written don't get published because they are not considered good enough.

Many get submitted to the wrong publishers - for example a sexy romance submitted to a publisher specialising mostly in children's books is going to be rejected, and the market is difficult these days for writers of Regency romances because sales have dropped. It is enough to do something that doesn't fit in with the publisher's guidelines when submitting a manuscript, for example not including a cover letter, not going through an agent (this can land the manuscript in the slush pile, to be read at convenience, which could mean months or years), or sending in something that is too long or too short (for example, it's common for category romance publishers to request that manuscripts be no longer than can be fitted on 150 or 200 pages of a trade paperback).

Sometimes it seems to be pure luck that something gets published.

What is more puzzling to me is how most of the books published actually get chosen and not trashed.

It appears that there are an amazing number which should never merit ink on a page!

My theory is that in many cases, poor books get published because the author knows the right people. Good books get rejected because the author doesn't know anyone in the field. It's all about who you know. Most publishers won't glance at a book unless it is represented by an agent. Finding an agent, again, unless you know someone who knows someone who's step-brother is in the business can be very difficult. I know this is a very pessimistic view of the industry, but I think it is all in the connections. Stephen King's wife and son are both published writers... is the son any good? Have you ever read his stuff? Likewise, S.K.'s wife was published before he was and took S.K.'s manuscript of Carrie to her agent. Would he have been able to find an agent on his own without her connections? We will never know.

The days of tossing book manuscripts over the transom are gone. There are too many unsolicited manuscripts and the people reading "the slush pile" are the lowest guys on the totem pole. Over-worked and under-paid. I say that it is akin to breaking into modeling or the movies these days. Yes, unknowns DO get in, yes, unknowns do become successful, but when a big money-maker like John Grisham comes to you and says, "Hey, my cousin wrote a book that should be published.", you tend to do what he wants because he brings in so much cash for you and ignore the unknowns because you've only got the money and the time to publish a finite number of books. (this is just an example and not based on any facts at all.) And it's no longer about publishing the best books, but the books that will make the most money. And I tend to think of RP-ers as the minority of readers who look for both content and quality of writing... we are not necessarily the mainstream.

Just my two little pennies.
PAM

Another important reason books don't get published--even very good books--is that there has to be a fairly large market for the book and the topic to make it financially worthwhile for the publisher, especially in this sad age when fewer and fewer people are reading.

I still believe that a good book can find a publisher--but it has to be good and the author will probably have to settle for a small publisher or university press, and then do most/all of the marketing him/herself.

My best advice is to create a published track record for yourself thru articles in magazines, journals, newspapers. A previously published author is much more likely to get a book contract.