The problem is not that white backgrounds get dirty easily or that it is difficult to determine the correct exposure, although both of these things are true. Instead the problem is U.S. Patent 8,676,045. Yes, that is right, Amazon has successfully patented using a white background when photographing subjects. For more on this controversy see Photographers howl at Amazon patent of decades old idea and Amazon’s ridiculous patent makes Mark Cuban happy.
May 28, 2014: The Professional Photographers of America provides more details on Amazon’s patent at Hear About Amazon’s Patent on Studio (Lighting) Arrangement? Here’s What it Means for You.