Upload & Sell: On
But let me go out on a limb and suggest one reason why: I think the color versions appear on the high end of contrast, crunchiness, and saturation towards slightly unnatural rendering. Could be subjective post choices, or working on an uncalibrated monitor (mine is calibrated), or a combination of the two.
B&W sometimes shines when the colors go funky/hardcore, and can work at harder contrast/deeper, crunchier blacks where color won't.
In the color versions, I see a strong yellow/green cast and the hard processing-- which distracts me from the actual stuff in the image. In the B&W versions, I am only seeing the subjects and not having a conversation with myself about the colors.