Shallow DOF for stock
1. Lens are a little less than optimal at wide apertures, leading to potential rejections. Macro lenses (such as used in my cookie shot) are exceptions, but most fast lenses will introduce color fringing in out of focus areas.
2. Maximum flexibility, more sales. If a designer picks an image that is sharp throughout they can selectively defocus areas, or isolate the background, etc. If you have blurred edges it is hard to do isolations after the fact. I think an image with thin depth of field has a more restricted market.
3. Bokeh - it can be tricky to get pleasing out of focus areas depending on the lens and aperture. In stock a simple background is better so I usually try to find a simple background rather than try to blur it out.
Give me some examples of images with thin DOF that work for you, or arguments for and against :) I love portraits with shallow depth of field, but I just don't use it much for stock.
Photo credits: Brad Calkins.