As a reader, I love a series. I enjoy reading a series with the same characters and seeing how they evolve. A good example, J. Frost's Night Huntress books with Cat and Bones. In other books/series, I enjoy reading about the different characters and their struggles. Good examples include Kerrelyn Sparks' Love At Stake series and Kelley Armstrong's Otherworld series. In the former, each book is about a different character, yet involves other important players that show up in all the books. And those other characters eventually get to tell "their" story in a book in the series. Great idea. In the The Otherworld series, one book may be about werewolves, and another about a witch or demon, yet they are all tied together in the same world, in this case "Otherworld" and have a challenge to face. Books with these two series could easily stand-alone.
In my Soul Catcher series, my characters are pretty much the same in each book. They evolve and the protagonist has to face some kind of challenge. I have 4 books in that series and I grew very close to them. I could probably keep it going for a very long time, but there's so much more I long to write.
In my new series, I decided to try something new. I created a paranormal world and the people "moving" into the community (or already "moved" in) will have a book and will have some kind of relationship challenge. So each will stand alone, yet will be part of a large series. (I hope large—lol). Since this is new for me, I hope it works. I'm halfway done and my goal is to finish the first book this year, then submit it in Dec, maybe January. We'll see what happens.
Why do I write books in a series? Because that's what I read and what I like. Plain and simple.
I have to admit that my ideas are mostly large scale ones and that plays a part in why I write books in/for a series too. Sure, I have a couple ideas for single novels, but I tend to get attached to my characters or their world, which makes me want to develop the books into a series. It's a difficult decision for me to make (which book to write) when I have several ideas jumping up and down in my head. Based on what I like to read, you can guess what my selection will be.
Are you a series lover too?