It involves a bit more, you have to take orders, keep tabs on the dining room, run around balancing a bunch of stuff, interact with people, smile at patrons and smile at the sous chef who calls you a whore or a queer every time you pick up. In contrast, being a cook in most kitchens is like being an assembly line worker. The "grill cook" literally just stands over a grill flipping stuff. You don't have to ever speak to anyone or even need to know english. (I was a grill cook in a busy restaurant once)

I'm not saying being a server is worth 2x as much as a cook but I can see how they could get paid more. In the same vein a bartender makes hella ducats more than either a server or a cook and most of the time they are just serving beer or vodka & cranberry drinks.