Fast food is a crazy example they point to. You'll spend 12-15 dollars a person easily at fast food places these days, and they serve hundreds of customer an hour. Giving the entire staff a $15/hr raise would be an extra 2-4% to the cost of a meal.

If you have 5 employees working the shop and average 100 meals an hour, you're looking at an extra $0.75 per meal to give each employee and additional $15/hour - which is a life-changing raise at a cost customers wouldn't even notice.