Most hourly jobs with the public, especially corporate ones, calculate labor costs and try to keep them as low as possible. They estimate the minimum staff that can handle the maximum traffic, and try to shoot for that goal. One nameless corporate coffeehouse where I worked took this to the extreme. It always felt like we were juuuuuust shorthanded enough to be constantly on our toes/slightly behind, at all times. This way, if one person wasn’t pulling their weight, everyone else hounded them until they kept up. Otherwise, everything went totally to shit and everyone suffered.
In an environment like this, you have to make sure someone covers you if you take a bathroom break or get supplies from the back. Taking a sick day is pretty much unheard of. If nobody will cover your day, the whole operation goes out of whack. The pressure comes from the top down, from the corporate office to the management to the staff. There doesn’t have to be a policy about a sick note- the culture alone is enough to make people feel like they have to come in.
And @Bellatrix is right, most jobs with the public don’t have paid sick leave. A lot of them don’t have health insurance either, so the employees can’t afford to go to the doctor. So if a doctor’s note is required for a sick day, that sick day could leave the employee several hundred dollars in the hole. If you earn nine bucks an hour, it’s a lot easier just to work through the sick day.
It’s not right that people do this. Especially in food service, they could potentially sicken hundreds of others. But for those workers, there isn’t a lot of choice.