I have often wondered that. Same in super markets and Bunnings. Staff all wearing steel caps. Many customers in thongs and soft toes.
lots of steel wheeled trolleys and heavy objects moving at even walking pace can crush and really hurt.
in a plane it's likely some idiot in thongs will block exit as he or she realises they are ill-shod a d may get a scratch or prickle if there is vegetation or debris near where they are going to get off the slide.
Getting out of a plane in an orderly but prompt manner can be life and death for 100's. These are low probability high consequence situations.
