If sex sells why don't I write it?

Erotic romances.

Before I go further, let me state that I am not a prude as I have written two erotic romance short stories. 

Several years ago, I got offered the opportunity for a contract to write erotica; the problem was that the remit of the firm was open and I found myself questioning the boundaries of what I could write, and for how long?

I did try to write a story but writing a story based on sex I found upsetting to the point I was physically ill. Other than that, I would find it hard to write a story where sex is the central theme.

Some of my stories have sex in them, but the sexual aspect is part of the story, not the central theme of the writing.