It only takes a few extra seconds or minutes. After a customer service call, leaving a gas station with the receipt, Amazon delivery (I know some of you still use them come on).
It helps employees in brutal industries get bonuses, promotions, and a mental health boost for a moment of your time. And many of their reviews are from those old and angry enough to take the time to complain.
I've never been in customer service but it just seems like the human thing to do.