With home equipment, if you try to reduce too large a volume of juice and sugar to jelling consistency, you run the risk of over cooking, since you have to cook so long. You then end up with crystals which make the jelly cloudy. It can also have the effect of caramelizing, giving the jelly a honey texture with a burnt or over cooked taste. Even if it doesn't cloud, it can become tough. (Been there.) 6 cups at a time is the accepted limit, 4 cups for a really fine product. There are always exceptions, though.

A similar thing might happen when you double or even try to triple a fudge recipe. The texture just isn't right!! Preserves and conserves can generally be done in larger amounts. The limiting factor with preserves is the delicate nature of the fruit, such as strawberries, which might be crushed with the handling.