You've tried -- for months, or for years -- to convince a literary agent to persuade a traditional publisher to lend its imprint, and its credibility, to your book because you're under the impression that book promotion opportunities exist for traditionally published books that aren't available for self-published titles.
Wrong.
Here's the good news. For the most part, the stigma that used to be associated with self-published books is gone. While traditionally published books have lost none of their cache, even with all of the changes in the published world, new opportunities have arisen for those whose books haven't been picked up by traditional publishers. While the traditional publishing world was doing its thing (the same old, same old thing, for the most part), self-published books (and that includes self-published ebooks, by the way) have established their own strong track records and earned their own top-notch book promotion opportunities.
To reinforce my point, here's an interesting link from -- ironically enough -- a venue that's all about traditional publishing (but that, in recent years, has begun to take self-published authors seriously, too).
This Publishers Weekly article shares the results of a recent Writer's Digest survey that compares writers' (those who have worked with traditional publishers to publish books and have also self-published their own books) satisfaction with traditional traditional publishing compared to self-publishing. Self-publishing came out ahead, and I believe it's because self-published authors gain so much (specifically, monetary rewards and control over every aspect of their work) and sacrifice so little by way of media recognition, credibility, and distribution/sales potential.
In short, it's as easy to find book promotion opportunities for self-published books as it is to find book promotion opportunities for traditionally published books once you look beyond book reviews (some of which are still unavailable for self-published authors since some traditional book review outlets are still holding onto the last vestiges of discrimination against self-published books).The book promotion opportunities for all books, and ebooks, have grown in number over the years as new venues have emerged. All books, and ebooks, regardless of the way they are published, have access to these book promotion opportunities.
Now it's just up to you, the author, to find those book promotion opportunities, and to see how your book can take advantage of them.
