There are many good reasons for converting an image to black and white. Some images contain a lot of contrast and texture which can be better emphasized in black in white. Others have historic content that fits well with historic black and white looks. And sometimes an image is part of a series, and the best way to bring the entire series together is to process them all similarly in black and white.
But in the case of the image above, the main reason for conversion may not be apparent at first glance. Photographers have limited tools for controlling the color in their images. In some cases the only practical control of color is the veto: remove all chromatic information, and work from there. A look at the original image below should be enough to explain the reasoning in this case. It might make a good shock value image in color, but removing the bright tones certainly simplifies the image.
C. David Tobie