We never gave it a thought. We were probably too busy cleaning our shoes with it (that too free of cost). But in reality, the escalator brush exists for a far better purpose that concerns your safety. 

You might have come across in news about accidents caused due to escalators when people get too close to the edges. If you notice carefully, every step of the escalator has a yellow border drawn, which is apparently a warning to keep distance from the sides. 

What about the brushes though? They help prevent accidents. The yellow borders are definitely a visual warning but the bristles that give a sensation to your feet whenever you get close to the edge, trigger our subconscious into action. You immediately shift in the middle when you feel the bristles touching your shoes. It also tends to keep passengers’ luggage or other items away from the skirt (gap). 

So, if you’re not paying attention, the escalator brush might prevent you from doing anything dangerous without you even realising it. 

And please, don’t clean your shoes with those brushes, it absolutely kills the purpose and also risks your life.