Should the writer be thinking about marketing while writing? HAHAHAHAHAHAHAH! Sorry, that was the poet in me laughing. This is me thinking about marketing after I’ve finished a poem: “I wonder if Mark will like it….”
Book marketing, generally speaking, falls on the shoulders of your publishing team. So while marketing shouldn’t be your primary focus, you do need to be mindful of it. In terms of your work’s “marketability,” I’ll explain it this way. An editor I knew would often speak of her desire to acquire books that hit a “sweet spot.” She meant that she was looking for books that checked off a number of desired categories. This could include hot trends and genres (think Fifty Shades of Grey and Gone Girl), as well as books that dealt with timely issues.
While that may be how she evaluated the books that crossed her desk, many writers don’t write thinking about sweet spots. That’s because the creative process is often messy and doesn’t always fit neatly into categories. Nor should it, IMHO.