Questions about 16R (and maybe 11R)

I'm sure we've all seen the pictures of 16R for sale with it's Bigazzi livery, but lacking sponsor logos. Could someone please tell me why they keep the paint colors, but not the sponsor logos? I think it would look better if it were kept the same as it came off the track. Do laws for converting them to street cars force them to remove all the logos?

11R isn't really the same since it's solid orange rather than black/orange, but I would prefer the track version look with the Frank Muller logos, too.