Clare Vanderpool received 60 rejection letters before Moon Over Manifest was published and then won the 2011 Newberry Medal. What's up with that? What goes on in the publishing world that such a fine novel would be rejected by 60 editors/agents?
It's a cold, hard equation of what kinds of book sales can be generated from a topic. Some fantastic pieces of literature are simply ahead of their time. Others get lost and go unnoticed in the giant piles of manuscripts. Beauty is in the eye of the beholder, and one man's masterpiece may be another man's pulp fiction.
The intense competition in the publishing world with the advent of audiobooks, online books, digital readers and the like have made publishers more cautious than ever with their print media publications, but also more adventurous when it comes to publishing people online, since there is little risk and overhead costs involved.
The previous post hit the nail right on the head. Publishing costs are higher than ever and sales of print material have fallen ever since the rise of online reading sources. Profit-making is still the publishing world's foremost goal, not producing superlative literature from unknown and untried authors.
There is an economic factor at play in publication decisions and many of the big publishing houses are more concerned with marketability in conjunction with quality. That is not to say that great writing doesn't get published, but publishers are looking at what is making a "best-seller" these days.
It is the case far too often. Stephen King was rejected repeatedly before his first novel was published; I'm sure those publishers regret their decision. As accessteacher posted above, there are many factors besides the writing itself that go into deciding if a book is published. The major determining factor is money. Will the book sell? Publishers are interested in the business of selling books and not really in the literature itself.
Once a book is published, it is looked at from a different perspective. Newberry Medals are given for literary quality and technique; they are not based on how many copies sold.
Unfortunately, I feel that the publishing world today is driven more by factors that are not relevant to whether a given book is good or not. Factors such as world events, seasons and even what other books have been published recently determine whether publishers will accept a book. Unfortunately, as in the case you have identified, this results in authors having to be very persistent when trying to get their work published.