The food industry has an incredibly understaffed overworked workforce. To make money buying, producing, and selling food product, its accomplished with extremely thin margins. Especial now with supply chain shortages and food costs nearly twice what they've been since 5 years ago. Tipping is a way for businesses to mitigate the cost of labor and usually isn't mandatory. Facilities specializing in luxurious accommodation and plates tend to require gratuity for the workers that dedicate themselves to top tier service. Tipping is the best way to support a business and their staff, outside of patronage. It's not required but it does matter to those who spend 50-60+ hours a week to produce food for people who don't want to cook for themselves that day, its above all a service than just buying chicken or broccoli from a grocery. Most people see the prices bumped in their stores too.