Steve, no one is saying that a horse-rider can never randomly loose an object (when he goes to reach in his pocket to get something as he's riding, etc...) along a random BFE trail. But what we're talking about here is : Wisely spent time.
Example: There was 2 stage stops, within about 2 miles of each other , on the incoming CA emigration trail, here in CA. 1 served as a main intersection-fork-in-road stop, and the other was a dude who hung out his shingle and had a "store" of sorts. Both were stopping spots for the wagon road traffic. And between these 2 spots is still, to this day, the faint line of a dirt road between them (the original "route" of the westward ho emigrants).
And my buddy and I (who have found lots of period coins and targets at each location) have mused the SAME thing you're musing: "Gee, there ought to be some random losses along the wagon road too !" So on a few occasions we start following the old dirt road/path. And as soon as we're 50 or 100 yards from the ground zero stage stops, it goes sterile. And after 30 min. of fanciful wanderings, we "wake up" and realize that we are doing LOTS better to hunt where all the people stopped for the night. Slept, ate, spent $ at the store, etc.... Does that mean if you wander BFE forever that you might eventually find something random ? SURE ! But where is your time better spent ?