It was more about name "gruel" because it reminds me some french friends..
there were many vegetable dishes that were in use for ages and then dissapeared with growth of commercial foods or became less popular. But some of them still exists and they are usually considered "tradicional" in some way, because of an old ege of that dish in meaning of recipe. Like what you would probably called "sauerkraft soup". Before all that commercial packed foods people knew more about nutrition of vegetables, and they used what was available.. and knew how to preserve it.