Actually the push for designated cooks began in the US Army in the mid-1800s (if not sooner)...mainly to improve the quality of food and cut down on wastage (as the position used to be rotated among men in a company and as a result quality was uneven at best). It's also worth remembering that one of the most frequently identified reasons for desertion in the Old Army was the number of construction and other work details piled on the troops. Many said they joined to be soldiers, not to build forts or dig ditches. Officers at the time complained loud and long about this, to no result.

Food is, of course, important. I'm surprised no one mentioned Napoleon's maxim about armies marching on their stomachs... At the combat small unit level, units do tend to eat together (unless they have serious internal problems), and those patterns have never shown many changes. Likewise, soldiers will always complain about the food. It's in the contract somewhere....