Upload & Sell: Off
Another reason for many doing this is lighting.
During the morning prep there is usually lots of mixed lighting, tungsten, daylight, fluorescent etc...
Most don't want to spend too much time trying to balance it out, black and white fixes that easily
But B&W have always been a great nature of wedding photography, even though we shoot digital and in great color nowadays, B&W gives that nostalgic feeling to a lot of viewers.