In his book, "Common Kingsnakes, A Natural History," Brian Hubbs recommends "feeding at least every week, if not more often. Twice-weekly feedings will ensure the animal stays healthy and grows. Two food (prey) items are sufficient for each feeding..."
My female is a voracious eater from March to late October - at which time she refuses food, and is placed in brumation till the following February. She'll be 5 years old next June, is 5 feet long, and weighs 1453 grams. She is still smaller than the largest King of her species found in the wild. And I'll posit that "typical modest sizes of specimens found in the wild" is due to abbreviated longevity (it's tough out there), and the associated challenge of regular predation.
My feeling is that many keepers may feed more conservatively because they keep a large number snakes, and for them, it's simply a matter of economics. I'll also add that my King gets considerable exercise by way of supervised yard time - which also helps me keep cage-cleaning to a minimum.