No offence, but how does physically coming to you and bringing your food justifies paying additional 10-20%? As mentioned above, I live in EU and almost never t

No offence, but how does physically coming to you and bringing your food justifies paying additional 10-20%? As mentioned above, I live in EU and almost never tip, because I cannot really understand this cultural thing. Why should I pay a special tip to sbd who brings my food and not clerks in a bakery or a garbage track drivers? I'm being serious here, I'm trying to understand why people do this. Is there any other reason than "the custom"?