Look at road racing some 99% of riders where white shoes, it's the fashion I guess?
Back to CX however dull race conditions are virtually all riders wear sunglasses at the start , many will be discarded mid race, that's for the sponsors?
I get roadies doing it as they like to pose with the one bit of kit they get to decide for themselves, but even they question their choices on a day when its wet & grimey, as they know they'll get wrecked.
For CXers, and it was basically the majority of riders in both races, knowing the course conditions. It just seemed insane because no matter how hard you try to clean them, they'll always have some dirt left on them and they'll just fade to grey.
And you might imagine top riders get sponsored to do it, but not half the flipping field wrecking 200quid plus shoes just to look "fashionable".