Nick11, That is a good "rookie" question.
Keep in mind that in order to set a buried trap that the ground is going to get disturbed in the process to begin with. The fresh sifted dirt over the trap, blended in or not, is attractive to canines, as well as other critters when combinations of lure, bait and urine are used at that fresh looking patch of soil.
It functions as an added visual element of curiosity to entice a fox to investigate and work the set. I have caught many red fox while on location at a dirthole set with exposed fresh soil contrasting with green grass in a hay field without using any lure, bait or urine.
The habitats illustrated in my photos were taken about a week before the season, and will change very little, with the exception of crop removal until all is buried in snow. The crop fields (hay, corn, soybean,) meadows, wooded edges and brush piles are virtual rodent factories where fox and coyotes hunt for food.
To give you an idea about what you have questioned, here are two examples from your fellow PA trappers.
Study the location and habitat types in this photo. Do they look at all similar to any of those I presented earlier in this thread?
This coyote was caught in PA not many days ago by T-man member
Magnum Hunter using a dirthole set in the hay field.
Master fox trapper, Phil Brown from PA, catches more red fox than any other man that I know with this season's catch for evidence:
And, this is the set Phil catches most of them in:
Those should help answer any questions you may have had about disturbed sod and contrasting fresh soil exposed at a fox/coyote set.