Next time you land on a contaminated runway, then taxi is “slush” to the gate at midnight, for the jet to sit til the 6am departure…. It’ll make sense. Spent 5 years on that puppy, only a handful of times had to actually leave flaps out, but it made sense when it occurred.

Behind the tires (and shoved up into the flaps) would be a snowcone of yuckiness, frozen, into the extended flaps.