[John Jarrold]

Because it's incredibly unusual for an author to write in one genre to a commercial standard. And each genre is separate. Just because an author can write fantasy wonderfully, if doesn't follow that he or she can also write SF, humour, crime or anything else to a high, commercial standard. They each exercise different muscles

The words publishers live by in 2008 are 'Life's too short'. Any author not willing to stick to one genre and work at it over a career is usually consigned straight into that bin. And as I have said elsewhere: of course there are exceptions, but they ARE exceptions.