The truth is, even a best-seller will barely net a livable wage -- and unless you get extremely lucky to stay up on the charts chances are you're like 90% of all the other authors out there and your books just won't keep their momentum.
This forces writers to try and produce multi-part series... in the hopes of generating a renewed interest with each new installment of the series... but even so, full-length novel series, like my BITTEN novels, take a lot of time to plot and write well. They are detailed storylines epic in scope, and I can only write one novel like that in a year (at the most two).
This leaves me with either publishing short stories in anthologies or writing novellas. I have personally chosen to go the route of novellas since I am a creator at heart and a storyteller. I always have 3 or 4 ideas bopping around in my head and this way I can get more of my story ideas down onto paper. Furthermore, it becomes easier to produce ongoing series, or serial episodes so to speak (which is hugely popular in television right now), and I hope to experiment with genre and styles to find something that cliques with readers.
Also, it's worth noting that in this age of digital publishing, readers want instant gratification. Digital publishing has, to an extent, forced novels to become even more disposable of a medium. People download a book, read it, and then want the next one ASAP!
In the end, it just makes more logistic sense to write short, fast, installments in novella form instead of writing a 100K novel that takes over a year to produce and which is only capable of making enough back to cover production costs. Writing a series of novellas over the course of the year -- each 17K to 20K -- and each quicker and cheaper to produce than your standard novel ensures that the author can make back production cost. At least that's the hope, anyway. It's worth a shot.
So, that said, here's my next planned novella: Valandra: Vera Causa. My goal is to have it ready for a November release, after which I will clamp down on getting Robotica finished.