- You have not written the right book.
- You have not sent the right book to the right publisher.
- You have not sent the right book to the right publisher in the right way.
- You have not sent the right book to the right publisher in the right way at the right time.
What is the right book? The right book is any book which the editor can convince the marketing department that they can convince the sales department that they can convince book-sellers that they can convince readers to buy. The right book is a great book or a popular book or a fresh-voiced book or a book on a topic so sensationally interesting that lots of people (or enough people) would want to buy it. Not in the opinion of you or your grandchildren or your best friend's friend, but in the expert (though not infallible) opinion of the professionals in the publishing industry. What you think doesn't matter - it's what you can make them think that does.
What is the right publisher? The one that publishes or wants to publish the sort of books you've written. Supposing you go to a bookshop to research which publishers publish books like your fantasy series about dinofairies, and supposing you find that Edgar Allen Pickles & Co never have, do NOT think to yourself, "Ah, they don't, so maybe they should - I know, I'll send them mine and they'll LOVE it." No they won't, because if they wanted to publish fantasy they would. So, research which publishers like your genre. This applies equally whatever type of book / reader is yours.
What is the right time? Ah, that's when luck comes in a little bit, though do try to avoid bandwagons when they've already passed in a flurry of dust. (And remember that your book if taken today is probably up to two years from hitting the shelves). You can be unlucky and send something to a publisher which has just filled its list, taken something similar to yours, decided never to touch dinofairies EVER again. Or you can be lucky and send just what they're looking for.
What is the right way? That's easy. That's the bit (see the piece on Inexcusable Ignorance) about reading all the stacks of advice on the topic, in places like the Writers' and Artists' Yearbook and publishers' / agents' websites. Rules may be made for breaking but don't break their rules, except one: when they say they're not taking new submissions or unagented work, ignore them - if yours is great, they want it. I'm adding an article on submitting work soon, which will add to your knowledge. But get genned up first.
Many unpublished authors think that their work is brilliant and that the agents/publisher who have rejected them are stupid and ignorant. No, they're not. They can be wrong but even if they don't want your book, for good commercial reasons, they'll spot your talent if you've got it and they'll make suitable nice noises. If you haven't been accepted yet, you simply haven't written the right book (etc etc) or shown your talent, or perhaps found your voice, and you have to face that and decide what you're going to do about it. You have to deal with it, not by moaning about ignorant publishers but by ruthlessly and analytically working out what you are doing wrong. And putting it right. And if it can't be put right, you won't be published.
I strongly suggest you read the article on COMMON MISTAKES BY UNPUBLISHED AUTHORS.