Here's a few reasons why I think they've become popular:
- Digital book sales and print-on-demand offers from companies makes it a lucrative business in that the publishers don't spend a lot of money on the printing part of the process (the author spends none). I believe the reader pays for the printing in the price of the book and yet these books are still priced the same or lower than self-published print books.
- They can choose specific niches that are in demand--romance, speculative, dystopian, etc. They can be selective in only taking the genres they want. This is great for genre specific authors.
- This is a solution to the indie book quality problem. There are very good self-published books, but there are also some terrible ones where not much editing was done or money spent to make it professional. By it going through an indie press, it will have been edited and given professional attention. (I'm not attacking self-published authors, but recognizing the fact there is no filter to measure quality which makes it vary).
- It allows publishers to take on new aspiring authors and work with them on a smaller, personal, hands-on basis. It becomes a community. It is a collaborative process, whereas some authors describe Big 5 methods as sometimes impersonal and controlling (no personal experience, based off reading other authors' experiences).
- These indie presses may swallow up some of the self-published industry. A few recent articles are claiming the decline of self-publishing has started; others argue it's plateauing naturally after a massive boom. Either way, as long as books sell, more of these publishers will thrive. We may even see more "middle" presses develop--successful and growing large in the amount of titles published but not a Big 5.
- They are limited in how many books they release a year, so to meet the demand, more presses are springing up. Most seem to release 8-10 books a year on average. This means they will have a focus. It makes it easy for you to target them for queries.
- They take chances on, sometimes preferring, new authors. They usually try to attract them which is quite opposite of the Big 5 who want a resume of book titles and/or an agent. This made it clear to me that if I wanted to be published (and I could never afford to self publish properly), I would take that chance.